Operation Of Static Synchronous Compensator Research Articles

Reactive power management in variable frequency transformer (VFT)‐integrated multi‐machine power systems: A STATCOM‐based approach

AbstractIn 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.

A Critical Review of Modular Multilevel Converter Configurations and Submodule Topologies from DC Fault Blocking and Ride-Through Capabilities Viewpoints for HVDC Applications

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.

Cascaded H-bridge Based STATCOM With Improved Ride Through Capability of Submodule Failures

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.

Seven Level Voltage Source Converter Based Static Synchronous Compensator with a Constant DC-Link Voltage

Flexible alternating current transmission system (FACTS) controllers are important to enhance the quality of power in power systems. The stability of a system is achieved via a FACTS device (a Static Synchronous Compensator (STATCOM)). This paper aims to control the losses in the transmission system during peak energy demand circumstances with minimal losses in the economical and functional efficiency of the system. The STATCOM operation of a seven level voltage source converter (VSC) with binary-weighted transformers is proposed for controlling the reactive power variations and terminal voltage changes at dynamic circumstances in the transmission system. The STATCOM is operated at 132 kV and is a 50 Hz AC system with a single DC-Link capacitance and two VSC power circuits. Each VSC circuit consists of three H-bridges with specific switching angle control in order to achieve low total harmonic distortion at the fundamental frequency. The coupled control circuit phenomenon is imperative for computing the switching angle for a stable performance. The dynamic functional improvement efficiency is harvested with a minimum number of switches and transformers used in high voltage and high-power applications. The number of switches, transformers, and capacitors for 132 kV are optimized with a proposed STATCOM operation in seven level VSC with binary-weighted transformers. The simulated results prove that the proposed model significantly improved system performance and stability.

Dynamic Stability Improvement of Power System by Means of STATCOM With Virtual Inertia

The paper investigates the application of Static Synchronous Compensator (STATCOM) with synchronverter control to enhance dynamic stability. Synchronverter is a control strategy for voltage source converters that emulates a synchronous generator, therefore providing virtual inertia. A thorough analysis of system stability with STATCOM controlled using synchronverter is presented. Furthermore, a comparison to vector control is provided. The analysis was conducted for a commonly known Single Machine Infinite Bus (SMIB) test case. The authors also compare the synchronverter and vector control performance using different mathematical tools such as eigenvalue analysis, numerical simulation, and lyapunov theory. Synchronverter algorithm improves the damping of the system, as small-signal analysis shows. The results of numerical simulations demonstrate the improvement of dynamic stability. Besides, the stability region also improves in the case of synchronverter. Finally, the paper demonstrates on the IEEE 39 bus system that the operation of STATCOM with a synchronverter control strategy is feasible and improves dynamic stability. Synchronverter brings the advantages of artificially adding inertia to the system, an essential issue in modern power systems.

Wide-Area Measurement-Based Adaptive Backup Protection for Shunt Compensation Environment

In this paper, the localization issue associated with distance relay protecting a transmission line with static synchronous compensator (STATCOM) is discussed. Generally, distance relay is mal-operated due to the dynamic behaviour of STATCOM during its inductive and capacitive modes of operation. Because, STATCOM operation creates the problem of correct measurement of fault distance and is responsible of under-reach and over-reach of distance relay. Furthermore, high fault resistance is also the reason of under-reach along with STATCOM operation. To overcome aforementioned challenges, an adaptive wide-area backup protection scheme (WABPS) is addressed which compares the calculated impedance and referenced impedance. Calculated impedance is the difference between impedance measured by relay and impedance contributed by fault resistance. Referenced impedance is the sum of fault impedance and impedance contributed by STATCOM. If calculated impedance is less than referenced impedance, then the relay will generate a trip signal. Proposed WABPS is inherent directional and provides information about fault detection, fault distance, and fault resistance during dynamic operation of STATCOM. The performance of the proposed WABPS is evaluated using technology of synchronize phasor measurement and communication channel. A 230 kV, 50 Hz system with a 24-pulse STATCOM is simulated and validated using PSCAD/EMTDC software package.

IMPACT OF REAL AND REACTIVE POWER CONTROLLABILITY OF STATCOM ON TRANSMISSION LINE PROTECTION

Static synchronous Compensator (STATCOM) is a shunt connected Voltage Source Converter (VSC) based FACTS controller which is useful in improving the voltage regulation. VSC based FACTS controllers facilitate connection of energy storage devices like battery, fuel cell, Super Magnetic Energy Storage(SMES) etc. at the DC bus. Addition of energy storage device results in better real and reactive power flow control, transient stability enhancement and power oscillation damping. However, FACTS controllers with energy storage device in the line poses new challenges for the line protection device. Operating region of STATCOM with energy storage device (STATCOM – ES) encompasses all the four quadrants in P – Q plane. Impedance contribution by STATCOM operating in any of these four quadrants can modify apparent impedance seen by distance relay and hence needs to be investigated thoroughly. Main aim of this paper is to analyze the impact of emulated conductance and susceptance by four quadrant operation of STATCOM on the performance of distance relay in a hybrid compensated system. A novel control strategy to dynamically modify the reference for real power exchange by STATCOM is proposed to avoid damage to the STATCOM during fault. Possibilities of distance relay under reach and over reach due to operation of STATCOM - ES in various operating modes and impact of fault resistance on the relay performance is discussed.

Directional relaying in presence of STATCOM during single pole tripping

Static synchronous compensator (STATCOM), a shunt type flexible AC transmission system device, is used to control the voltage at different locations within a power system by absorbing/injecting reactive power. The dynamic control action associated with the operation of STATCOM in both capacitive and inductive modes is the reason for varying system condition and failure of different relaying schemes. Directional relaying is affected by the reactive current contributed by STATCOM in wide range of inductive to capacitive mode of operation. Further, single pole tripping (SPT) condition during STATCOM operation leads to mal-function of the directional element due to phase change in sequence components of voltage and current. In this study, directional relaying is addressed for different types of faults in the presence of STATCOM connected at different locations during single phase auto reclosing period. Proposed directional relaying technique is based on the phase angle between positive sequence fault and pre-fault apparent powers. Performance of the proposed scheme has been investigated for different types of faults for single and double circuit lines during SPT using simulated data of different power networks using PSCAD/EMTDC software. A comparative study is also carried out to verify the performance of the proposed scheme for different STATCOM operating conditions.

Reactive Power Strategy of Cascaded Delta-Connected STATCOM Under Asymmetrical Voltage Conditions

Cascaded static synchronous compensator (STATCOM) is an effective solution for reactive power support in middle/high voltage conditions, and it has been widely employed to control reactive power in photovoltaic (PV) plants, wind farms, and industrial occasions. In this paper, reactive power control strategy of cascaded delta-connected STATCOM under asymmetrical voltage conditions is investigated. A new phase current reference calculation method is proposed to support reactive power continually under abnormal voltage conditions considering cluster voltage balancing control and phase current limitation. Constrains between voltage and current phasors of STATCOM are deduced. Then, the analytical expressions of phase currents and circulating current references are solved. Therefore, reactive power support and the safe operation of STATCOM can be obtained simultaneously by limiting the peak value of the phase current references. Furthermore, the reactive power support capability of cascaded STATCOM under asymmetrical voltage conditions is explored and compared by combining the proposed references calculation method with the three generalized current references calculation strategies. Finally, simulation and experimental results have been given to verify the theoretical studies.

STATCOM Operation Scheme of the CDSM-MMC During a Pole-to-Pole DC Fault

In this paper, a static synchronous compensator (STATCOM) operation scheme of the modular multilevel converter adopting clamp double submodules (CDSM-MMC) during a pole-to-pole dc fault is proposed. By analyzing the current paths of a CDSM, this paper proposes three new operation states of the CDSM, which allow the CDSM to provide bipolar voltages when the arm current that flows through it is negative. Through control of the CDSMs to operate in these new states along with the blocked state, the arms of the CDSM-MMC can operate alternately in two different modes, that is, the conducting mode and blocked mode even when the dc-link voltage drops to zero. Thus, the CDSM-MMC is capable of working as a STATCOM during a dc fault. Moreover, a control strategy of the dc-fault STATCOM operation mode is designed to control the reactive power provided by the CDSM-MMC, to limit the dc fault current, and to reserve and balance the energies stored in capacitors. Simulation results conducted in PSCAD/EMTDC demonstrate the validity of the proposed STATCOM operation scheme and control strategy of the CDSM-MMC during a pole-to-pole dc fault.

Impact of static synchronous compensator on flux‐based synchronous generator loss of excitation protection

In order to increase the power transfer and providing the optimum utilisation of the power system capability, application of flexible alternating current transmission system (FACTS) devices technology, such as static synchronous compensator (STATCOM), has been attracted, in recent years. However, the STATCOM changes the voltage and current of the power system that disturb the operation of the impedance-based synchronous generator loss of excitation (LOE) protection. Then, this study proposes a new flux-based LOE protection method, in the presence of STATCOM, that is based on the local variation of the flux linkage of the generator available at the location of relay. The mentioned relay is independent of other generator protection relays without any coordination. In order to show the satisfying operation of the proposed method, some simulations have been carried out in the Matlab/Simulink software. A single-machine infinite bus and a three-machine infinite bus systems have been used in simulations. The results show that the presence of STATCOM has no important effect on the performance of proposed relay opposite to a negative offset relay with two protective zones (the widely used impedance method) which is affected by STATCOM operation.

DC fault ride‐through capability and STATCOM operation of a HVDC hybrid voltage source converter

High voltage direct current (HVDC) transmission systems are becoming increasingly popular when compared to conventional AC transmission methods. HVDC voltage source converters (VSC) can offer advantages over traditional HVDC current source converter topologies; as such, it is expected that HVDC-VSCs will be further exploited with the growth of HVDC transmission. This study presents the DC fault ride through capability and new static synchronous compensator (STATCOM) modes of operation for the recently published alternate arm converter, intended for the HVDC market. Operation and fault ride through of the converter during a local terminal to terminal short circuit of the DC-link is demonstrated; during the fault STATCOM operation is also demonstrated.

Design of Robust Current Controller for Two-Level 12-Pulse VSC-based STATCOM

The static synchronous compensator (STATCOM) is a shunt connected voltage source converter (VSC) based FACTS controller using GTOs employed for reactive power control. A typical application of a STATCOM is for voltage regulation at the midpoint of a long transmission line for the enhancement of power transfer capability and/or reactive power control at the load centre. The PI controller-based reactive current controller can cause oscillatory instability in inductive mode of operation of STATCOM and can be overcome by the nonlinear feedback controller. The transient response of the STATCOM depends on the controller parameters selected. This paper presents a systematic method for controller parameter optimization based on genetic algorithm (GA). The performance of the designed controller is evaluated by transient simulation. It is observed that the STATCOM with optimized controller parameters shows excellent transient response for the step change in the reactive current reference. While the eigenvalue analysis and controller design are based on D-Q model, the transient simulation is based on both D-Q and 3-phase models of STATCOM (which considers switching action of VSC).