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Summary: The non‐permanent dc short‐circuit fault is a crucial issue in overhead high voltage dc transmission (HVDC) lines. In this paper, a cross connected (CC) cell also known as hexagonal switch cell (HSC) based modular multilevel converter (MMC) with dc short‐circuit fault ride through feature is addressed for an HVDC system. During normal operation, the CC cell‐MMC is capable of producing an identical number of levels while using fewer power devices than full‐bridge (FB) and clamp double sub‐module (CDSM)‐based MMCs. Similarly to the FB‐MMC and CDSM‐MMC, the provided CC cell‐MMC not only blocks the dc fault current but can also function as a static synchronous compensator (STATCOM) during a DC‐Bus fault. The Proposed control technique uses MMC as a STATCOM to inject reactive power during a pole‐to‐pole DC‐Bus fault to keep the grid stable. The control approach comprises injecting zero‐sequence voltage into each phase to balance the mean voltage of capacitors and arm currents. The fundamental zero‐sequence voltage is obtained by a simple stationary reference frame‐based controller. The control strategy's efficacy is evaluated in MATLAB and confirmed in the Opal‐RT environment. [ABSTRACT FROM AUTHOR]

In order to improve power system stability and suppress low power oscillations, active power regulation using variable frequency transformer (VFT) plays an important role. The literature has already documented in‐depth research on active power transfer control principles of VFT. The VFT, which is basically a wound rotor induction machine consumes reactive power because of magnetizing winding. In terms of the power flow interchange in a two‐area power system incorporating VFT, this work gives an extensive analysis to comprehend the reactive power needs under various operating circumstances. In the context of reactive power compensation, the present study explores two distinct methodologies: the implementation of a fixed shunt capacitor and the utilization of an artificial neural network (ANN)‐based static synchronous compensator (STATCOM). The STATCOM‐based control technique outperforms the conventional fixed shunt capacitor by demonstrating improved capabilities in reducing reactive power imbalances and stabilizing the power system. Further, a control scheme based on voltage regulation is implemented for integrating the STATCOM to enhance the fault ride through capability of a three‐phase bus fault. Additionally, two‐area test system is exposed to a reactive load shift to evaluate the operation of STATCOM, which restores the bus voltage to its pre‐specified value. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive performance analysis of power systems incorporating High Voltage Direct Current (HVDC) transmission lines, with a focus on the impact of integrating advanced Flexible AC Transmission Systems (FACTS) devices, namely Static Synchronous Series Compensator (SSSC) and Static Synchronous Compensator (STATCOM). This study evaluates key performance parameters, including Total Power Loss (TPL), Voltage deviation (Vdev), transmission efficiency, and corona loss, across three configurations, HVDC alone, HVDC with SSSC, and HVDC with STATCOM. Through simulations conducted using MATLAB or Simulink, the results demonstrate that the addition of SSSC and STATCOM significantly improves system performance by reducing power losses, enhancing voltage stability, and optimizing transmission efficiency. The analysis reveals that HVDC systems with SSSC outperform other configurations in terms of power loss reduction and voltage stability, while STATCOM improves voltage regulation and minimizes deviations. This study highlights the benefits of incorporating SSSC and STATCOM into HVDC systems for enhancing power system efficiency, stability, and operational reliability. [ABSTRACT FROM AUTHOR]

This paper purposes to demonstrate the effectiveness of fuzzy logic controller (FLC) over proportional integral (PI) controller for reducing the fault current and maintaining the voltage profile at different faults conditions using Static Synchronous Compensator (STATCOM) which is considered an effective FACTS (Flexible Alternating Current Transmission System) device. The study evaluates the performance of a power system equipped with STATCOM which is connected in shunt with bus B1 under various faults conditions, including single-phase and three-phase faults. The performance of the STATCOM is evaluated by using two different controllers: PI controllers and FLCs. A comparative analysis is done between the performances of the two different controllers using Matlab/Simulink software package. The results obtained conclude that the presented system gives better performance with STATCOM as compared to not using it under several faults conditions besides, the STATCOM gives better response with FLC as compared to PI controller. It is demonstrated that STATCOM with FLC can reduce the positive sequence fault current at bus B1 to 96.49% of its value without using STATCOM under line to ground fault and 98.17% under three line to ground fault whereas STATCOM with PI controller can reduce it to (99.57, 99.05%), respectively. Also, the bus voltage B1 is improved to 102.19% by using STATCOM with fuzzy controller under line to ground fault and 101.86% under three line to ground fault whereas STATCOM with PI controller can improve it to (100.21, 100.93%), respectively. [ABSTRACT FROM AUTHOR]

With the increasing penetration of microgrids in distribution systems, the possibility for voltage variations increases. This paper proposes the use of a static synchronous compensator (STATCOM) fed by a DC microgrid to control the voltage of a 3-phase AC distribution grid and provide bidirectional active power transfer from the AC grid to the DC microgrid and vice versa. A simplified control is applied to this system to manage the magnitude and angle of the system voltage at the point of common coupling. With the use of a PI controller and pulse width modulation, the proposed control was able to modify the active and reactive power compensation. The control approach is characterized by its simplicity and rapid response to system changes, such as fault occurrences or load variations. The proposed control system is applied after converting the 3-phase system into a dq system to simplify the voltage regulation process. The PSCAD package is used to perform the simulation. Results demonstrate that it is possible to control STATCOM to offset reactive power and regulate grid voltage. The results validated the ability of active power transfer through the line by injecting negative and positive active power. The transfer of active and reactive power from the AC grid to the DC microgrid, and vice versa, is examined in this study following the STATCOM rating and the energy management demands. [ABSTRACT FROM AUTHOR]

In this paper, a comparison between Flexible Alternating Current Transmission System (FACTS) devices including Static Synchronous Compensator (STATCOM), Static Synchronous Series Compensator (SSSC) and Unified Power Flow Controller (UPFC) for providing a better adaptation to changing operating conditions and improving the usage of current systems. The power system using FACTS devices is presented under different conditions such as single phase fault and three phase fault. A digital simulation using Matlab/Simulink software package is carried out to demonstrate the better performance including the voltage and the current of the presented system using FACTS that located between buses B1 and B2 under different faults types. The results obtained investigate that the presented system gives better response with FACTS as compared to not using them under abnormal conditions besides, the UPFC gives better performance of power system under several faults as compared to STATCOM or SSSC as It can absorb reactive power in a manner which significantly reduced the fault current. It is demonstrated that UPFC can reduce the peak fault current at bus B1 to 63.85% of its value without using FACTS devices under line to ground fault and 79.18% under three line to ground fault whereas STATCOM and SSSC reduce it to (75.21, 94.35%) and (75.40, 94.68%), respectively. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To build a large-scale renewable energy integrated system in the power system, power fluctuation mitigation and damping measures must be implemented during grid connection. PID damping controllers and traditional intelligent controllers with pole configuration are usually used for improving damping. Integration of large wind power plants and photovoltaic power plants into the power system faces transient power oscillation and fault ride-through (FRT) capability under fault conditions. Therefore, this paper proposes a static synchronous compensator (STATCOM) damper based on a recurrent Petri fuzzy probabilistic neural network (RPFPNN) to improve the transient stability of the power system when large offshore wind farms and photovoltaic power plants are integrated into the power system, suppress power fluctuation, and increase FRT capability. To verify the effectiveness of the proposed control scheme, a three-phase short circuit fault at the connected busbar is modeled in the time domain as part of a nonlinear model. From the comparison of simulation results, the proposed control scheme can effectively slow down the transient fluctuation of power supply to the grid-connected point when the grid is faulty, reach steady-state stability within 1–1.5 s, and reduce overshoot by more than 50%. It can also provide system voltage support at an 80% voltage drop and assist in stabilizing the system voltage to increase FRT capability. It also improves stability more than PID controllers when disturbances are present. Therefore, it maximizes the stability and safety of the power grid system. [ABSTRACT FROM AUTHOR]

This paper aims to improve the voltage profile using the Static Synchronous Compensator (STATCOM) in the power system in the Kurdistan Region for all weak buses. Power System Simulation studied it for Engineers (PSS\E) software version 33.0 to apply the Newton-Raphson (NR) method. All bus voltages were recorded and compared with the Kurdistan region grid index (0.95≤V ≤1.05), simulating the power system and finding the optimal size and suitable location of Static Synchronous Compensator (STATCOM)for bus voltage improvement at the weakest buses. It shows that Soran and New Koya substations are the best placement for adding STATCOM with the sizes 20 MVAR and 40 MVAR. After adding STATCOM with the sizes [20MVAR and 40MVAR] at Soran to the test, it is seen that the total average change in voltage profile for the system improved results in about 17.34 % in average per unit change for the 28 weakest buses, which provides a good improvement in stability. Also, the system’s total active power loss reduced from 123.8 MW without STATCOM to 102.8 MW with STATCOM. The results are encouraging for applying the approach to the power system. This approach stands out due to all bus voltages are within acceptable ranges.

The intelligent substations should be developed to perform multifunction operations, including power flow control, voltage regulation, and cost-effective power quality (PQ) improvement. In this article, an intelligent substation by a distribution transformer integrated with a capacitive-coupling winding tap injection static synchronous compensator (CWTI-DSTATCOM) is proposed for balance and unbalance operations. Compared with the state-of-the-art approaches, CWTI-DSTATCOM can operate at a low dc voltage with a small active inverter rating, which also can provide distributed voltage, reactive, and unbalanced current compensation. The power rating reduction mechanism is mathematically revealed via balance and unbalance compensation analysis, which is further used to determine the optimal inverter power rating of unbalance operation via an optimal LC filter design method. Furthermore, a comprehensive compensation control strategy is developed to coordinate the transformer taps and the active inverter under balanced and unbalanced operations. Simulation and real-time digital simulator hardware-in-the-loop experiments are performed to prove the validity and effectiveness of the proposed topology over inverter rating reduction and PQ enhancement. [ABSTRACT FROM AUTHOR]

The distance relay using the transmission line impedance measurement identifies the type and location of the fault. However, any other factors that cause the failure of the measured impedance, makes the relay detect the fault in incorrect location or do not detect the fault at all. One of these factors is the fault resistance which directly increases the measured impedance by the relay. Another factor that indirectly alters the impedance of the transmission line is static synchronous compensator (STATCOM). When a fault happens, current injection by the STATCOM changes the measured signals by the relay and thus makes the calculated impedance incorrect. In this paper, a method is provided based on the combination of distance and differential protection. Firstly, from the current data of buses, faulted transmission line is detected. Then using the presented algorithm, the fault location is calculated on the transmission line. The basis of the algorithm is on the active power calculation of the buses. Fault resistance is calculated from the active powers and its effect will be deducted from calculated impedance by the algorithm. Furthermore, with choosing data of appropriate bus, STATCOM effect is eliminated, and fault location will be obtained. [ABSTRACT FROM AUTHOR]

Electric arc furnaces (EAF) produce light flicker (LF) by injecting inter-harmonics in the frequency band vicinity to the fundamental frequency of the power supply system. LF seriously affects the efficiency of manpower by irritating, and the machines by causing the fluctuations, which results in heavy economic loss to the customers. Its compensation also burdens with large economic value. In this work, the band of inter-harmonics responsible for LF is calculated mathematically. EAF current has inter-harmonics components, which vary with the flicker frequency. Hence, flicker frequency is varied in the standard range from 0 to 20 Hz and a Fast Fourier Transform (FFT) analysis of the EAF current is done to determine the magnitude and frequency of inter-harmonics components present. The analysis reveals that the inter-harmonics in the range of fundamental frequency ± 20 Hz (maximum flicker frequency) are contributing to the LF. The LF is compensated through STATCOM by modifying the Instantaneous Reactive Power (IRP) Theory-based control algorithm to compensate only the inter-harmonics of the above-mentioned range. The effect of the strategy is the considerable reduction in the capacity of STATCOM with the LF level coming under the prescribed standard limits. MATLAB/SIMULINK and real-time environment results verify the usefulness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Dynamic compensators, such as active power filter (APF) and static synchronous compensator (STATCOM), can be used to mitigate the low-frequency oscillations (LFO) in high-speed railway vehicle-grid systems. However, the small-signal impedances of APF and STATCOM are affected by that of vehicles, which makes it challenging to characterize the impedance of these devices directly and ensure stable operation. The traditional stability analysis is based on terminal impedances of source and load subsystems, which does not always provide sufficient insight into LFO suppression. In this article, a novel idea based on $dq$ -frame admittance decomposition is proposed to investigate the impact of APF and STATCOM on the system stability. The proposed approach is demonstrated in simulation and experimental results. It is shown that the control paths of the APF and STATCOM for measuring the vehicle current introduce their coupling with the vehicle. The resulting coupling admittance of these devices plays a significant role in the load admittance reshaping and determining their ability to enhance the system stability and suppress the LFO. [ABSTRACT FROM AUTHOR]

This paper presents a novel inter-cluster direct current (DC) capacitor voltage balancing control scheme for the single-star configured modular multilevel cascaded converter (MMCC)-based static synchronous compensator (STATCOM) under unbalanced grid voltage. The negative-sequence component of grid voltage at the point of common connection (PCC) causes unbalanced active power flow in the phase limbs of converter. This leads to the imbalance of DC voltages of the submodule capacitors across the MMCC phases, and consequently, the malfunction of converter. The proposed solution is to inject both negative-sequence current (NSC) and zero-sequence voltage (ZSV) into the phase limbs of MMCC. A quantification factor QF is used to achieve the sharing of intercluster active power between the NSC and ZSV injection methods. Accurate determination of the quantification factor has been presented. In addition to maintaining the DC voltages of sub-module capacitor across the MMCC phases balanced, it also prevents the overcurrent and overvoltage of converter by injecting NSC and ZSV with the right proportion. The control scheme is validated on a 3.54 kV 1.2 MVA power system using MMCC-based STAT-COM with 3-level bridge cells as sub-modules. The results show that the proposed scheme provides superior effectiveness in eliminating the voltage imbalance of DC capacitor in the phase limb while maintaining low voltage and current ratings.

In this article, we introduce a model predictive control with optimal switching sequence (OSS-MPC) for a multilevel static synchronous compensator (STATCOM). The studied STATCOM is based on a hybrid multilevel inverter named HC-FNPC formed by the cascaded connection of H-bridge cells with a full-bridge neutral point clamped cell (FNPC). In this article, the optimal switching sequences are derived for HC-FNPC STATCOM by considering the impact of each switching sequence on the voltage of capacitors. Then, the control objectives of hybrid multilevel STATCOM, i.e., ac current control and capacitors’ voltages balancing, are formulated in terms of OSS-MPC for the first time. In contrast to the conventional MPC, this method provides a fixed-switching frequency. Also, by a combination of optimal switching sequences in MPC, the regulation of capacitors’ voltages with unequal values is realized. The control system's performance is verified on a nine-level (9L) 2.4 Mvar/11 kV HC-FNPC STATCOM in MATLAB/Simulink. Also, the experimental results are provided on a 9L 1.25 kvar/220 V scaled-down hardware prototype. [ABSTRACT FROM AUTHOR]

Steel production worldwide continues to grow and, consequently, also the energy consumption of the steel sector. With the applications of the electric arc furnace route in the steelmaking process, the concern with aspects of power quality and overload of the transmission grid lines increases. This work presents the zero harmonic distortion (ZHD) converter static synchronous compensator (STATCOM), which makes it possible to increase the displacement power factor of an electric arc furnace (EAF) application from 0.88 to 0.98 with total demand distortion in the grid around 1.44% with the ZHD prototype operation, this being accomplished without using high-order sinusoidal filters and with consolidated components in the industry. [ABSTRACT FROM AUTHOR]

A single‐delta bridge‐cell converter (hereinafter referred to as an SDBC converter) is a prospective power converter for a static synchronous compensator (STATCOM). The authors have proposed a dc/3ϕ power converter using the SDBC converter and a medium‐frequency single‐phase transformer with an operating frequency of 150 Hz; this converter can exchange a maximum active power of 37% of the rated reactive power with three‐phase ac mains supply without increasing the voltage and current ratings of the SDBC converter. In particular, the negative‐sequence reactive power control is a challenging task because of the high magnetizing inductance of the transformer. To achieve the negative‐sequence reactive power control, a single‐phase transformer with low magnetizing inductance is applied to the converter at the expense of the exchangeable active and reactive power. The relationship of the magnetizing inductance, active power, and reactive power is revealed in this paper, and the operation of the converter under low magnetizing inductance is experimentally verified by employing a downscaled 110‐V, 7‐kVA model. [ABSTRACT FROM AUTHOR]

In the event of a DC side fault in modular multilevel converters (MMCs), the fault current contributions are initially made by submodule (SM) capacitor discharge, which occurs before the fault is detected, followed by the AC side contribution to the DC side fault. While the AC side currents can be regulated using fault blocking SMs, the initial discharge of the SM capacitors results in high DC fault currents, which can take several milliseconds to be brought under control. This paper presents a method to actively control the rate of rise of the DC fault current by regulating the discharge of SM capacitors and accelerating the suppression of fault current oscillations during fault ride-through (FRT) in a full-bridge (FB)-MMC system. In the proposed method, the discharge direction of the FBSM capacitors is reversed following the detection of a DC side fault, which leads to a reversal in the fault current direction and a fast drop-off towards the zero-crossing. Immediately after the zero-crossing of the DC fault current, the DC fault is cleared by adjusting the arm voltage references and operating the MMC as a static synchronous compensator (STATCOM) to provide voltage support to the AC grid. The proposed control scheme provides faster fault current suppression, more effective SM capacitor voltage regulation, low AC side and MMC arm current transient peaks, and an overall superior DC-FRT performance compared to methods in which the conventional fault ride-through operation is initiated immediately upon DC fault detection. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) based on half-bridge submodules (HBSMs) are unable to prevent the AC side contribution to DC side fault currents, thus necessitating circuit breakers (CBs) for protection. A solution to this problem is using submodules (SMs) that are capable of blocking the flow of current from the AC grid to feed the DC side fault. The full-bridge submodule (FBSM) is one type of fault blocking SM where the presence of two extra switches ensures that in the event of a DC fault, the reverse voltage from the FBSM capacitor is placed in the path of the AC side current feeding the DC side fault through the antiparallel diodes. However, the additional semiconductor switches in the FBSMs increase the converter cost, complexity, and losses. Several SM configurations have been proposed in recent years that provide DC fault blocking capability with lower losses and device counts than those of FBSMs. Besides, many of the proposed hybrid converter configurations that combine different topologies to optimize converter performance are also capable of providing DC fault blocking. Furthermore, certain SM topologies are capable of riding through DC faults by remaining deblocked and operating in static synchronous compensator (STATCOM) mode to provide reactive power support to the AC grid. In this paper, noteworthy SM and MMC configurations capable of DC fault blocking and ride-through are reviewed and compared in terms of component requirements, semiconductor losses, and DC fault handing capability. The review also includes a discussion on control strategies for MMC arm/leg energy balancing during STATCOM operation. [ABSTRACT FROM AUTHOR]

This paper presents a new power electronic topology for a STATCOM allowing the generation of multilevel AC voltages. This topology is characterized by a modular configuration since it uses two well known four-leg two-level voltage source inverters. A Scott transformer with multiple secondary windings connects the two four-leg inverters to the grid. One of the important features of the proposed power topology is the capability to generate AC voltages with high number of levels, in spite of using only two four-leg two-level voltage source inverters. To maximize the number of voltage levels a geometric progression ratio of 3 between the windings of the transformers connected in cascade is proposed. However, to reduce the turns-ratio span, alternatively a fractional geometric ratio of 1.5 is also proposed and analyzed. A control strategy adapted to the proposed power converter topology is also presented. Besides the control of the reactive power the regulation of the four-leg inverter DC voltage will also be considered. To support the theoretical studies and assumptions, simulations and experiments are presented. Experimental results were obtained using a low power laboratory prototype. The results shown give evidence to the characteristics and features of the proposed power converter topology and control system. [ABSTRACT FROM AUTHOR]

This article proposes a thyristor-based T-type converter with modular multilevel dc-link (TTC-MMD), where the thyristor-based T-type converter provides the basic phase commutation capability and two arms of cascaded submodules in dc-link generate the multilevel switching line voltages. To guarantee the successful turn-on and turn-off of thyristors, one full-bridge submodule (FBSM) is embedded in each arm. In addition, the FBSM can also be employed to participate in the multilevel switching modulation. For real applications, the TTC-MMD can be employed as a medium-/high-voltage static synchronous compensator, which features triplen frequency fluctuation of capacitor voltages and easy balancing of capacitor voltage under various operation conditions due to the common dc-link shared for three phases. It can also be implemented in other medium-/high-voltage applications. Finally, simulation and experimental results verified the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

The rapid developments in the technology, industrial revolution and growing population stimulated the demand for energy. Fossil fuels have dominated energy sector for many years. But the situation is rapidly changing due to climate changes trigged by greenhouse gas emissions of fossil fuels and fast depletions in the reserves of fossil fuels. This has forced the policy makers to encourage use of renewable energy instead of fossil fuels. The use of grid integrated wind turbines has been increasing at a greater pace, leading to power quality problems in the grid. In this a paper, a STATCOM control scheme is proposed to mitigate the power quality problems posed due to grid integration of wind turbines. Power Balance Theory (PBT) is employed to generate reference currents for grid synchronization. Another advantage of the proposed scheme is to obtain the desired Unity Power Factor (UPF) and Total Harmonic Distortion (THD) in the system at the desired levels with a reduced switching frequency of the IGBT switches of the STATCOM. The proposed system along with control scheme is simulated in MATLAB/SIMULINK. To highlight the reduced switching frequency capability of proposed Space Vector Current Controller (SVCC), a comparative analysis is also performed with simple two step On-Off Current Controller (OOCC) and the results have been presented for both the controllers for the purpose of comparison. [ABSTRACT FROM AUTHOR]

The fixed-impedance-based distance relaying schemes find limitation in providing reliable protection to transmission lines connecting doubly fed induction generator based large capacity wind farms and compensated with static synchronous compensator (STATCOM). In this article, the performance of the distance relay protecting such transmission lines is investigated and proposes an advanced protection scheme where the fault detection and fault section identification task is performed using the signs of the superimposed $\alpha$ -aerial components of the measured currents at the line ends and STATCOM location. Furthermore, suitable features are extracted from the relay end measured currents using dual-time transform (TT) and subsequently utilized by decision tree classifier for fault classification. Finally, the single-end traveling wave-based technique is employed using $\alpha$ and $\beta$ -aerial current waves for estimating the fault location. The performance of the proposed protection scheme is evaluated on different fault and nonfault cases generated on a two-bus test power system through MATLAB/Simulink and OPAL-RT (OP4510) manufactured real-time digital simulation environment. The performance of the proposed protection scheme is also compared with some earlier reported works. The demonstrated results justify the effectiveness of the proposed scheme for protecting such complex transmission networks. [ABSTRACT FROM AUTHOR]

Abstract A new inter-cluster DC capacitor voltage balancing scheme for a delta connected modular multilevel cascaded converter (MMCC)-based static synchronous compensator (STATCOM) is presented. A detailed power flow analysis of applying negative sequence current (NSC) and zero-sequence current (ZSC) injection methods in addressing the issue of inter-cluster DC voltage imbalance under unbalance grid voltage is carried out. A control scheme is proposed which integrates both inter-cluster methods using a quantification factor Q F . This is used to achieve the sharing of the inter-cluster active power between the NSC and ZSC injection methods. An accurate method of determining the quantification factor is also presented. The proposed method offers better sub-module DC capacitor voltage balancing and prevents converter overcurrent. The influence of unbalanced grid voltage on the delta connected MMCC-based STATCOM rating using this integrated cluster balancing technique is investigated. The control scheme is verified with a 5 kV 1.2MVA MMCC-STATCOM using 3-level bridge sub-modules, and the results show the advantages of the proposed method over other inter-cluster methods.

In this study, an investigation of different faults for a wind turbine–based doubly fed induction generator (DFIG) system is studied and the performance using a static compensator (STATCOM) is observed. The DFIG network is connected to a voltage source converter high-voltage dc link with a fault occurring near the wind generator network. The ride through capability of DFIG is promising with STATCOM using the proposed control strategy. The ac and dc voltage and torque oscillations are damped effectively, and improved power flow is observed. The low voltage AC grid fault occurs for an HVDC transmission, and the DFIG performance without and with STATCOM is compared, where the DFIG converter control schemes are developed using the proposed improved field-oriented control (IFOC) method. In this, the reference rotor flux value alters to a new synchronous speed value or a slighter value or a standstill depending on the stator voltage dip due to grid disturbance. This speed variation leads to introducing rotor current at that new rotor slip frequency as there is a change in the rotor speed because of the fault, which further decreases the stator flux dc component. Hence, this dc-offset constituent in the stator flux is alleviated and decays rapidly in scheming the divergence of the speed of the rotor to a new orientation speed with decay in the rotor flux. This operation is done in the inner control scheme of the rotor converter, which is quicker in response to the faults. Apart from this, the stator’s real and reactive power also changes accordingly based on the lookup table mechanism–based closed-loop control action of the pulse generator, and this power change is done in the outer loop. The analysis for DFIG and HVDC operation is verified under different faults without and with STATCOM.

Voltage instability and voltage collapse are the serious problems that can occur due to reactive power deficits caused by increased load or contingencies. Detecting potential voltage collapse in power systems is essential to maintain voltage stability during high demand. The stability of power systems is an important issue in the planning and operation of these systems. This paper determined the optimal location and size of a FACT STATCOM device for improving the static voltage stability margin of a transmission system. The study network is the IEE New-England transmission network. The problem has been formulated as a multi-criteria optimisation with the objectives of maximising load margin, minimising power losses and minimising voltage deviation. The objective function of the problem is adjusted using the analysis and optimisation method (CPF). The appropriate values and placement for STATCOMs are found using the CPF method based on the objectives below. The proposed method is verified using a simulation test on the IEEE-100 kV network which is part of the IEEE- 39 bus New England power system. The simulation results showed the efficiency of the CPF for the nominal values and the optimal location of the STATCOM. The results showed that the improvement of the voltage stability margin, the voltage profile of IEEE-100 kV is increased and the power losses are reduced. Finally, STATCOM ensures the overall stability of the transport network. [ABSTRACT FROM AUTHOR]

This article investigates the operation of cascaded H-bridge (CHB) based static synchronous compensator (STATCOM) after failure in its submodules (SMs). Once a switch fails, the corresponding faulty SM is bypassed. In the post-fault operation, a zero-sequence voltage (ZSV) is injected to the converter phases to generate the maximum possible line-to-line voltage. Using a clamping technique, the fundamental component of injected ZSV (FZSV) is minimized according to the operating point of CHB STATCOM. But, FZSV leads to unequal flow of active power into the converter phases. In the proposed method, negative-sequence current is controlled to manage the active power flow within CHB phases. By doing this, the effect of FZSV on active power of CHB phases is compensated and the voltages of capacitors are kept balanced. This method ensures the continuous operation of CHB STATCOM with the minimum over-design and guarantees the voltage balance of capacitors after a failure. The presented simulation and experimental results validate the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A type of peak-value dc voltage control (denoted as PK control) was proposed in the literature for supporting the use of a smaller dc-side capacitance when the single-phase voltage source converter is operated as a static synchronous compensator. Although it was demonstrated to operate stably under several conditions, it will be revealed in this article how the PK control will suffer from a more severe small-signal stability issue under nonideal grid conditions than the conventional method of controlling the average value of the dc voltage (denoted as Avr control). Especially, it will be shown how the PK control is sensitive to some of the control parameters. To obtain these results, a parameter-oriented stability analysis method is developed in the linear time-periodic framework. Then, it is utilized for parametric stability assessments of the Avr and PK control. Finally, both frequency- and time-domain experimental results verified the effectiveness and accuracy of the applied method in the presented analysis. [ABSTRACT FROM AUTHOR]

With the high penetration of the power electronic loads in the grid, the stability of static synchronous compensator (STATCOM) devices is greatly challenged. However, the conventional control methods for the modular multilevel converter (MMC) based STATCOM only consider the stability with small signal disturbances. This article proposes a novel dual-layer back-stepping control (BSC) for the MMC-based STATCOM. In the first layer, the BSC aims to regulate the sum of the capacitor energy and the reactive output current. In the second layer, the BSC aims to control the circulating current. Therefore, the proposed method possesses a fast dynamic response and accurate tracking with the Lyapunov stability of the MMC-based STATCOM. Compared with the arm-control-based BSC for MMC-based inverters, the proposed method has a simplified structure and a reduced computation burden. Moreover, the proposed method realizes the independent control between the output current and the circulating current. The simulation and experimental results verify the effectiveness of the proposed method. In addition, its robustness toward different circuit parameters and the operation ability under unbalanced grid fault is also verified. [ABSTRACT FROM AUTHOR]

Multilevel Voltage-Source Converters (VSC) based on modular structures are envisioned as a prominent alternative for grid and industry applications. Foremost among these are the Cascaded H-Bridge (CHB) and the Modular Multilevel Converter (MMC). In this context, depending on the application and the power conversion structure, unbalanced operating conditions can be asked to the converter. Previous investigations regarding the operation and the solutions for modular structures under unbalanced conditions have already addressed this topic, but information is dispersed over a wide number of sources. This paper identifies, classifies, and analyzes the intercluster active power balancing strategies for the adequate operation of the most commonly used modular structures in some typical unbalanced operating scenarios: the Static Synchronous Compensator (STATCOM) under unbalanced voltage and/or current conditions, the unequal power generation in large-scale photovoltaic (PV) power plants, and the uneven power distribution in a battery energy storage system (BESS). Each of the applications has been independently studied so as to provide a comprehensive analysis of the alternative techniques found in the specialized literature, clearly explaining their respective strengths and drawbacks. Several future challenges have been identified during the study, which will involve greater research effort in this key research topic.

The model predictive control (MPC) methods have been widely applied due to the fast dynamic performance and multiple control targets. However, they show certain limits when applied to the multilevel converters, such as unfixed switching frequency, large computation burden, and complex weighting factors selection. This article proposes a novel modulated MPC (M2PC) method for cascaded H-bridge (CHB) converter-based static synchronous compensator (STATCOM). Instead of multitarget integration and weighting factor design, the proposed method disintegrates the voltage balancing control process from the cost function. The evaluated control sets for output current control is decided by the search step and the search range in each period. By proper design and selection of the adaptive search step for the output voltage references under α–β coordinate, the search range can be reduced, which greatly reduces the number of evaluated control sets in each control period. Therefore, the dynamic of output characteristics and the low computation burden of the MPC method are guaranteed simultaneously. In addition, with the simple and independent integration of the capacitor voltage balancing control, the proposed method can be easily applied in the CHB converter-based STATCOM application. Furthermore, this article provides a delay compensation for the prediction process, and it provides a fixed switching frequency for each H-bridge cell. Simulation and experimental results verify the effectiveness of the proposed M2PC method. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a single-phase multifunctional electric-vehicle (EV) on-board charger with an advanced vehicle-to-vehicle (V2V) functionality for emergency roadside charging assistance situations. Using this function, an EV is able to charge from another EV in case of an emergency when the battery is flat and there is no access to a charging station. The designed EV charger can support the proposed V2V function with rated power and without the need for an additional portable charger. It can also provide conventional functions of vehicle-to-grid (V2G), grid-to-vehicle (G2V), the static synchronous compensators (STATCOM) and active power filter (APF) (i.e. reactive power support, and harmonics reduction). All the functions are addressed in the control part through the sharing of existing converters in an all-in-one system. The proposed EV charger is designed and simulated in MATLAB/Simulink, and a laboratory prototype is also implemented to validate its key functions.

This paper presents detailed implementation of static synchronous compensator (STATCOM) based on model predictive control (MPC) for mitigating unbalance in line voltages. The main objective is to evaluate the capability of an enhanced MPC state-space model that can be applied in a general form for any power system. The proposed enhanced MPC state-space model presented in this paper is adapted for mitigating unbalanced voltages at nominated buses by injecting suitable unbalanced currents and reactive powers by STATCOM. In addition, a proposed MPC objective function is developed and implemented to predict STATCOM injected output current according to line voltages of adjacent buses. This enables expecting the fluctuations from any part in the network to maintain nominated bus voltage at reference value. The results of MPC technique are compared with the same MPC technique developed for balanced line voltage mode.

A modular multilevel cascade converter based on single-delta bridge cells, hereinafter referred to as the single-delta bridge-cell (SDBC) converter, is a prospective power converter for a static synchronous compensator intended for voltage regulation and stability improvement of electric power systems. However, the SDBC converter cannot exchange nonzero active power with the three-phase ac mains unless energy storage elements such as batteries are connected to the dc side of each bridge cell. This article presents a dc/1 $\phi$ /3 $\phi$ power converter that combines the SDBC converter with a single-phase converter via a single-phase medium-frequency transformer with an operating frequency of 150 Hz. It can control the active power of 37% of the rated reactive power between the dc source and three-phase ac mains, thus enhancing voltage regulation and stability improvement. The operating principles and control method are first discussed, followed by a description of experiments using a downscaled 110-V, 5-kVA model. [ABSTRACT FROM AUTHOR]

In high power applications, 3-phase ac/dc Voltage Source Converters (VSCs) are paralleled to increase the overall aggregated converter power rating, effective switching frequency and control bandwidth. For this, interleaved Pulse Width Modulation (PWM) and current limiting paralleling inductors are required. Interphase Transformers (ITRs) are often used for the converter paralleling because they provide large magnetizing inductances for the currents flowing between the converters while introducing negligible leakage inductances for the currents flowing from the converters to the ac grid. This large asymmetry in the inductance values makes it difficult to independently control active power flows in the individual converters. Thus, if the converters dc buses are not mutually interconnected, instabilities in active control of balance of converter dc bus voltages can occur in certain operational conditions. This paper presents a theoretical analysis of the active power flows produced by the currents flowing among the converters and explains origins of potential instability in the active control of balance of dc bus voltages in multi-converter systems with floating dc buses, paralleled using the ITRs. [ABSTRACT FROM AUTHOR]

A new inter-cluster DC capacitor voltage balancing scheme for a delta connected modular multilevel cascaded converter (MMCC)-based static synchronous compensator (STATCOM) is presented. A detailed power flow analysis of applying negative sequence current (NSC) and zero-sequence current (ZSC) injection methods in addressing the issue of inter-cluster DC voltage imbalance under unbalance grid voltage is carried out. A control scheme is proposed which integrates both inter-cluster methods using a quantification factor QF. This is used to achieve the sharing of the inter-cluster active power between the NSC and ZSC injection methods. An accurate method of determining the quantification factor is also presented. The proposed method offers better sub-module DC capacitor voltage balancing and prevents converter overcurrent. The influence of unbalanced grid voltage on the delta connected MMCC-based STATCOM rating using this integrated cluster balancing technique is investigated. The control scheme is verified with a 5 kV 1.2MVA MMCC-STATCOM using 3-level bridge sub-modules, and the results show the advantages of the proposed method over other inter-cluster methods. [ABSTRACT FROM AUTHOR]

Summary: This work demonstrates the impact and robust coordination control among the Doubly Induction Generator (DFIG) and Synchronous Generators (SGs) with Power Oscillation Damping (POD), Power System Stabilizer (PSS),and STATic synchronous COMpensator (STATCOM) on the critical Low‐Frequency Oscillations (LFOs). These modes occurred due to system uncertainty, which leads to power flow interruption and experiences instability. It is mitigated by the proposed location and optimal coordinated optimized gain parameters of the controller. The locations are determined using the deterministic method and power flow sensitivity analysis (PSS and STATCOM). The objective function for the Genetic Algorithm (GA) is chosen as the real part and damping ratio of eigenvalue deviation of rotor speed. The small‐signal stability is assessed by using eigenvalue analysis via linearization of a nonlinear system. The transient stability is performed through time‐domain simulation by creating a three‐phase fault. Both analyses are examined with and without POD, PSS, and STATCOM and their combination by substituting SG with the same capacity of Wind Farm (WF). It is also indicated that a combination of POD, PSS, and STATCOM enhances system stability. It is also observed that the WF could not significantly involve in the modes of oscillation alike to the SG but provides the damping and beneficial toward the stability. GA and optimal location improve the system damping characteristics over a wide range of system uncertainty. The effectiveness and robustness of the proposed approaches are verified by considering a two‐area modified test system. Highlights: This work demonstrates the impact and robust coordination control among the DFIG and SGs with POD, PSS and STATCOM on the critical LFOs caused by the intermittent nature of wind power.The locations are determined using the deterministic method and power flow sensitivity analysis (PSS and STATCOM). The objective function for the GA is chosen as the real part and damping ratio of eigenvalue and rotor speed deviation.The obtained results show enhancement in system stability. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) based on half-bridge submodules (HBSMs) are unable to prevent the AC side contribution to DC side fault currents, thus necessitating circuit breakers (CBs) for protection. A solution to this problem is using submodules (SMs) that are capable of blocking the flow of current from the AC grid to feed the DC side fault. The full-bridge submodule (FBSM) is one type of fault blocking SM where the presence of two extra switches ensures that in the event of a DC fault, the reverse voltage from the FBSM capacitor is placed in the path of the AC side current feeding the DC side fault through the antiparallel diodes. However, the additional semiconductor switches in the FBSMs increase the converter cost, complexity, and losses. Several SM configurations have been proposed in recent years that provide DC fault blocking capability with lower losses and device counts than those of FBSMs. Besides, many of the proposed hybrid converter configurations that combine different topologies to optimize converter performance are also capable of providing DC fault blocking. Furthermore, certain SM topologies are capable of riding through DC faults by remaining deblocked and operating in static synchronous compensator (STATCOM) mode to provide reactive power support to the AC grid. In this paper, noteworthy SM and MMC configurations capable of DC fault blocking and ride-through are reviewed and compared in terms of component requirements, semiconductor losses, and DC fault handing capability. The review also includes a discussion on control strategies for MMC arm/leg energy balancing during STATCOM operation.

In the event of a DC side fault in modular multilevel converters (MMCs), the fault current contributions are initially made by submodule (SM) capacitor discharge, which occurs before the fault is detected, followed by the AC side contribution to the DC side fault. While the AC side currents can be regulated using fault blocking SMs, the initial discharge of the SM capacitors results in high DC fault currents, which can take several milliseconds to be brought under control. This paper presents a method to actively control the rate of rise of the DC fault current by regulating the discharge of SM capacitors and accelerating the suppression of fault current oscillations during fault ride-through (FRT) in a full-bridge (FB)-MMC system. In the proposed method, the discharge direction of the FBSM capacitors is reversed following the detection of a DC side fault, which leads to a reversal in the fault current direction and a fast drop-off towards the zero-crossing. Immediately after the zero-crossing of the DC fault current, the DC fault is cleared by adjusting the arm voltage references and operating the MMC as a static synchronous compensator (STATCOM) to provide voltage support to the AC grid. The proposed control scheme provides faster fault current suppression, more effective SM capacitor voltage regulation, low AC side and MMC arm current transient peaks, and an overall superior DC-FRT performance compared to methods in which the conventional fault ride-through operation is initiated immediately upon DC fault detection.

This paper presents a systematic procedure to design a simple control for a three-phase VSC-based static synchronous compensator (STATCOM) in order to overcome the problems caused by the presence of the non-linear load at the point of common coupling (PCC). The proposed control method regulates the STATCOM in such a way that the source quadrature current component is forced to be zero so that only the active current component is drawn from the source and the harmonic and reactive current demands of the non-linear load are met by the STATCOM. The tuning of the inner and outer loop PI controllers is carried out with the help of the modulus optimum and symmetric optimum criteria, respectively. At last, a few case studies are presented using MATLAB simulation to exemplify the success of the proposed control method.

This article proposes a novel capacitor-voltage balancing strategy for the double-Y modular multilevel converter static synchronous compensator operated under unbalanced current conditions of the system. The proposed method, based on zero-sequence voltage injection, manipulates the current distribution between the converter arms to minimize the converter ratings. The proposed balancing strategy is compared with the classical approach, based on controlling the circulating dc currents. For the same unbalanced conditions, the proposed strategy leads to lower energy rating for the converter as compared with the classical one, whereas the semiconductor ratings remain the same in both strategies. Theoretical findings are verified through experimental results. [ABSTRACT FROM AUTHOR]

This article develops a static synchronous compensator (STATCOM) based on the hybrid cascaded converter which has the advantage of reduced number of power transistors and floating capacitors compared to the cascaded H-bridge converter. A hybrid modulation scheme is employed in the hybrid cascaded converter to reduce the switching losses while maintaining the output performance, and the corresponding dc capacitor voltage balancing control scheme is proposed. The laboratory test results are provided to verify the feasibility of the developed STATCOM and the effectiveness of the proposed scheme. Furthermore, the proposed scheme is compared with the conventional scheme to reveal the improvement in output quality, power losses, and even fault ride through capability. [ABSTRACT FROM AUTHOR]

This paper presents an entirely new subject to prevent SSR in thermal power plants. The SSR phenomenon is firstly analyzed by using the frequency scanning method in the frequency domain under considering other operating conditions for operating grid-configurations, and then the SSR due to the self-excitation and the transient phenomenon is analyzed to provide the inputs for working out an effective solution. Three devices, namely the thyristor controlled series capacitor (TCSC), static synchronous compensator (STATCOM), and blocking filter (BL) are considered as a proposed choice, and the control strategy for each mentioned device is developed to mitigate the SSR. For TCSC, the control strategy is designed based on two PI controllers for the voltage and current regulator, respectively; besides, the auxiliary subsynchronous damping controller is proposed to provide a supplementary signal of dynamic current on the input signal that is chosen the generator rotor speed deviation. For STATCOM, two PI controllers, using for the DC and connected point voltage regulator, proposed; besides, the auxiliary sub-synchronous damping controller is proposed to provide a supplementary signal of dynamic current on the input signal that is chosen the generator rotor speed deviation. For BL, the natural torsional vibration frequency of models to ensure that SSR due to torsional interaction (TI), torque amplification (TA), and induction generator effect (IEG) are prevented. The effectiveness of this study is verified via a time-domain simulation of the Vietnam Quang-Tri electric power system connected to the 500/220 kV transmission system using EMTP-RV and PSS/E programs. The obtained results show that the frequency scanning method is chosen as a useful method to analyze SSR and the effective solution can be applied to immediately solve the difficulties encountering in the Vietnamese power system to be BL. [ABSTRACT FROM AUTHOR]

This article discusses development and verification test results of the 6.6-kV 200-kVA transformerless static synchronous compensator (STATCOM). This STATCOM is characterized by the use of a modular multilevel single-delta bridge-cell (SDBC) converter and silicon carbide metal-oxide-semiconductor field-effect transistor (MOSFET) modules. The article discusses a control method for the 6.6-kV system with focus on dc-capacitor voltage control. The voltage control presented in this article is different from the ones presented earlier. It consists of intercluster balancing control and intracluster balancing control. The former, also known as cluster balancing control, eliminates the requirement of the separate overall dc-voltage control present in conventional methods, whereas the latter, also known as individual balancing control, is replaced with a new technique based on the control of a dead time of each bridge cell. The article makes a detailed description of the latter. Experimental results obtained from the 6.6-kV 200-kVA verification test equipment validate the effectiveness of the control method. Moreover, successful test results confirm the efficacy of the system for grid-voltage regulation and load compensation. [ABSTRACT FROM AUTHOR]

This paper deals with a wind energy conversion system connected with grid. In this system rotor side and grid side converters are used to cope with reactive powers generated and to get the balanced output at the load side. A very effective control technique has been developed based on pulse width modulation to make the line voltages at the point of common coupling. Various filters have been used in this system and according to different filter parameters and design, the total harmonic distortion (THD) has been compared and calculated accordingly. [ABSTRACT FROM AUTHOR]

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In this paper, a transformerless distribution static synchronous compensator (DSTATCOM) based on the cross-switched (CS) multilevel inverter (CSMLI) is introduced. In comparison with the well-known cascaded h-bridge (CHB) topology, CS inverter produces higher number of voltage levels using fewer number of power components. Since CS inverter produces ac side voltage with high quality and has the ability to work at high voltage and power levels, the proposed CS-DSTATCOM is directly connected to the distribution grid without the need for a transformer. In the proposed CS-DSTATCOM, all the dc sources are replaced with dc capacitors. In this paper, an effective voltage balancing control scheme is proposed to keep the capacitors voltages balanced in the CS structure. The control scheme balances the capacitors voltages in two levels, i.e., inter-cell and within-cell level. On the other hand, the over-voltage and under-voltage phenomena are of the most common power quality (PQ) issues in distribution grids. The proposed DSTATCOM is able to cope with these issues by exchanging reactive power with the grid. Applying the CSMLI in the DSTATCOM structure as well as the capacitors voltage balancing methods are the main novelties of the paper. Also, the capacitors values are considered to be different (which is unavoidable in practice) while their voltages are balanced using the proposed voltage balancing methods. In this paper, a CS-DSTATCOM has been designed for 11 kV distribution grid and several simulation results are provided in the MATLAB/Simulink environment which validate the feasibility and performance of the proposed CS-DSTATCOM. [ABSTRACT FROM AUTHOR]