STATCOM Application Research Articles

Combining Proportional-Integral, Deadbeat, and Repetitive Current Controllers in Energy-Storage-Equipped STATCOM Application

Combining Proportional-Integral, Deadbeat, and Repetitive Current Controllers in Energy-Storage-Equipped STATCOM Application

Analysis of Cross-Connected Half-Bridges Multilevel Inverter for STATCOM Application

This paper suggested a single-phase cross-connected half-bridges multilevel inverter (cchb-mli) topology for static synchronous compensator (statcom) applications. The proposed mli structure consists of cross-connected multilevel cells connected in series with a more optimized number of devices to synthesize a higher number of voltage steps. Each cell in the structure consists of a set of switches and a dc-capacitor. Typically, when several dc-capacitors are used in an inverter, the dc voltages fluctuation occurs due to tolerance between passive element and asymmetric switch losses. A dual-loop control technique has been proposed with level-shifted pulse width modulation pwm to overcome these issues. The proposed methodology balances the dc-voltages using a proportional-integral controller by adjusting the switch duty cycle. The control method helps offset the issue of aggravated fluctuation while preserving the delivered reactive power distributed equally among the dc-capacitors at the same time. A thorough comparison is made between the proposed inverter concerning the number of components and efficiency to demonstrate the effectiveness of previous topologies. Moreover, a simulation model built in simulink and experimental results take from laboratory prototype to confirm the effectiveness of proposed structure and its control technique.

Power Quality Enhancement in Windfarm by using STATCOM

A FACTS (Flexible AC Transmission) controlled device, STATCOM is the best solution for power compensation in the area of microgrid system. It regulates the reactive power by injecting the reactive current in to the ac/dc hybrid microgrid terminals. The STATCOM is applicable for shunt compensation which has a great role in dynamic performance by controlling its reactive power. The proposed work demonstrated about the enhancement of voltage sag during fault condition. It can improve the wind turbine performance. The main objective for the STATCOM application in windfarm is to improve the system voltage by supplying or absorbing the reactive power into hybrid ac /dc microgrid system. During steady state operation, the fundamental component of the VSC (Voltage source converter) voltage in phase with system voltage, which shows uncontrol action on active power flow. If there is change between these two voltages (lead or lag), then STATCOM can generates (or absorbs) reactive power. This phase shift leads to flow of active power which is responsible for increase or decreases of capacitor voltage. Assumption has been taken by considering the fixed speed of wind turbine. The performance of windfarm with and without STATCOM is examined and analyzed under fault condition by using MATLAB Simulink 2016.

Digitalized Synchronization of Multi level STATCOM with Switch Fault Elimination

With much advancement in the FACTS technologies STATCOM with multi-level inverter provides reactive compensation with less harmonics injection in the grid system. The voltage stress on each power electronic switch is also reduced as the voltage across each switch is low, in turn reduces the switching losses. In this paper a cascaded multi-level inverter with STATCOM application of 2m+1 levels controlling through Space Vector PWM was considered. Switch fault analysis is carried out by detecting and mitigating the fault with a bypass power electronic switch. Design method and parametric analysis is carried out in MATLAB simulation and results arevalidated.

Evaluation of symmetric flying capacitor multilevel inverter for grid-connected application

Grid voltage regulation and reactive power control have been revolutionized by high-voltage high-power multilevel inverters (mlis) topologies. The implementation of such inverters in statcom application make it more feasible due to its multilevel output voltage, low harmonics, high modularity, and high-power quality. However, these topologies require more number of devices which adversely affect the overall system’s size, cost, and increase the control complexity. Recently, a packed u-cell (asymmetric flying capacitor) topology has been reported in literature with more output voltage levels using minimum number of components count. The conventional packed u-cell mli utilizes dc-sources to fed ac loads. In this paper, a symmetric flying capacitor (sfc) mli is introduced for grid-connected application. The proposed topology is suitable for medium voltage high-power grid-connected applications due to low voltage rating of switches. The sfc-mli utilizes dc-capacitors instead of dc-sources, therefore the inverter suffers from voltage imbalance problem. The voltage imbalance is due to non-ideal devices, asymmetric switching losses, and/or non-linear loads. Hence the capacitor balancing is relatively challenging task due to availability of limited number of redundant switching states. A multi-stage feedback control method is proposed with level-shifted (ls) pwm technique to address this issue. Furthermore, a comprehensive comparison in terms of redundant switching states and voltage rating of switches, has been carried out to highlight the superiority of the proposed topology over the existing packed u-cell topologies. In addition, the devices count, and components losses are studied. Finally, simulated and experimental results for different scenario are presented to validate the proposed topology and its control technique.

Comparison of DSCC and SDBC Modular Multilevel Converters for STATCOM Application During Negative Sequence Compensation

Among the various topologies proposed in this literature, the modular multilevel converter (MMC) is considered the next generation of converters for medium- and high-voltage applications. This paper presents a comparison between two variants of MMCs for STATCOM applications: The double-star chopper cell-MMC and the single-delta bridge cell-MMC. These converter topologies are compared and benchmarked during positive and negative sequence compensation. The comparisons are supported by analytical results regarding minimum effective dc-link voltage, number of cells, current rating, energy storage requirements, and operation during unbalanced conditions. The dynamic behavior, power losses, and cost of both solutions are evaluated through simulation model of a 15 mega volt-ampere (MVA) MMC STATCOM.

Selective Harmonic Elimination Technique With Control of Capacitive DC-Link Voltages in an Asymmetric Cascaded H-Bridge Inverter for STATCOM Application

In this paper, the selective harmonic elimination (SHE) technique is introduced for a cascaded H-bridge-based static VAR compensator (CHB-STATCOM) with unequal capacitive dc-link voltages. The asymmetric topology allows increasing the number of voltage levels while keeping the converter losses low. Moreover, reactive power control is realized by using the decoupled current control, and the voltage of individual capacitors is controlled by the help of SHE modulation. Mathematical equations are derived for synthesizing the multilevel ac waveform and regulation of dc-link voltages for a CHB inverter with an arbitrary number of H-bridge cells. Then, to verify the theoretical claims, simulation and experimental results are provided for a three-phase CHB inverter with two H-bridge cells in each phase.

Advanced Voltage Support and Active Power Flow Control in Grid-Connected Converters Under Unbalanced Conditions

Supporting the grid and improving its reliability have recently become major requirements for large distributed generation units. Under most grid faults, the accuracy of the traditional voltage support schemes (VSSs) is dramatically affected due to the existence of the zero-sequence voltage. Also, the traditional VSSs have been used only in the STATCOM applications, where the active power is zero. This paper proposes an advanced VSS in the converter-interfaced units, called zero-sequence compensated voltage support (ZCVS), to accurately regulate the three-phase voltages of the connection point within the pre-set safety limits. The proposed scheme not only compensates the zero-sequence component but also considers the active power injection. Unlike the traditional methods, the proposed VSS is adapted even in resistive distribution systems. The contribution of this paper is, however, ternate. As the second contribution, the limited active power oscillation (LAPO) is proposed to be augmented to the ZCVS. This feature limits the oscillation to a specified value which provides an adjustable dc-link voltage oscillation setting while simultaneously supporting the ac host grid, even under severe unbalanced faults. Third, the maximum active power delivery (MAPD) to the ac grid is also formulated for the ZCVS. The successful results of the proposed support scheme and complementary strategies are verified using selected simulation and experimental test cases.

DSCC-MMC STATCOM Main Circuit Parameters Design Considering Positive and Negative Sequence Compensation

The double-star chopper cell modular multilevel converter (DSCC-MMC) has been employed in several applications as HVDC, energy storage, renewable energy, electrical drives and STATCOMs. Generally, the DSCC-MMC main circuit parameter design presented in literature considers balanced currents flowing through the converter. Nevertheless, in STATCOM application, the converter can compensate negative sequence components and unbalanced currents flow through the DSCC-MMC, resulting in different stresses in the converter phases. Therefore, this work presents a detailed design methodology of the DSCC-MMC main circuit parameters, considering both positive and negative sequence current compensations. The dc-link voltage, number of submodules, power semiconductor thermal stresses, submodule capacitance and arm inductances are designed. Expressions for the energy storage requirements are derived when negative sequence is compensated. A case study considering a 15-MVA STATCOM is presented, and simulation results validate the proposed design methodology. Finally, the converter power losses and thermal stresses in the power semiconductors are evaluated.

Current Source Modular Multilevel Converter: Detailed Analysis and STATCOM Application

Multilevel current source converters are a smart choice for the high-power applications with low-voltage and high-current requirements. This paper presents the detailed analysis of a current source modular multilevel converter (CSMMC) and its application as a STATCOM. Various properties of CSMMC are compared with the voltage-source modular multilevel converter (VSMMC). The submodule inductance selection method and a sorting-based algorithm for inductor current balancing are proposed for CSMMC. The validity of the inductance selection method and the inductor current balancing algorithm are confirmed by the simulation of a three-phase CSMMC using PSCAD/EMTDC. The carrier phase-shifted sinusoidal pulsewidth modulation is used as the switching technique. The performance of a converter is analyzed with interleaved and noninterleaved carrier signals for the upper and lower arms. Results show that CSMMCs and corresponding VSMMCs have analogous features. Hence, the development on VSMMCs can be used for reference to CSMMCs and vice-versa. Furthermore, the control designs for CSMMC-based STATCOM are presented and verified using simulations. The obtained results of the proposed STATCOM show that the steady-state and transient performance of the system are quite satisfactory. This makes the CSMMC suitable for HVDC and flexible ac transmission systems applications.

STATCOM在500 kV北郊变电站的应用

随着电力电子技术的进步，STATCOM凭借着平滑的电压调节曲线和精确的调节能力，为电力系统电能质量的提高起到了重要的作用。本文以500 kV北郊变电站的STATCOM应用为例，对其运行模式和电压调节原理进行分析，通过实际运行情况，说明了STATCOM在电网运行中发挥的重要性和优越性。 With the development of power electronic technology, STATCOM has been playing an important role in improving the power quality of the power system with a smooth voltage regulation curve and a precise adjustment ability. This article takes the STATCOM application of 500kV Beijiao substation for example, analyzes the operation mode and voltage regulating principle, and describes the advantage and importance of STATCOM in power grid operation through the actual operation situation.

A Robust Fuzzy Sliding Mode Control Design for Current Source Inverter based STATCOM Application

This paper presents a robust fuzzy sliding mode control of a CSI based STATCOM. The dq-frame state space model is considered for nonlinear mathematical model for the system and controller design. A nonlinear fuzzy logic enhanced sliding mode controller has been proposed to provide active and reactive power control under various faulted operating conditions. Based upon the time domain simulations in MATLAB/SIMULINK environment the proposed controller is tested and it's better performance is shown compare with the conventional PI controllers with respect to voltage stability, damping of power oscillations and improving of transient stability.

Optimal Control of VSC for STATCOM Applications

Abstract In this work, a voltage source converter (VSC) is configured to perform STATCOM tasks and generate reactive power. An optimal H ∞ controller has been successfully implemented including an anti-windup compensator. Data from an experimental test bench is provided and compared with simulation results showing good accuracy level.

Voltage Source Converter Modeling for Power System State Estimation: STATCOM and VSC-HVDC

This paper presents new models of voltage source converters suitable for power system state estimation comprising STATCOM and VSC-HVDC applications. Both the back-to-back and the point-to-point VSC-HVDC variants are addressed. The state estimation models include DC measurements and converter control inputs resulting in an overall, seamless combination of the AC and DC devices or networks, in addition to providing for a higher degree of redundancy. Following a detailed description of all the relevant variables involved in the problem, taking into account equality constraints associated with both equipment and operation, a recommended set of state variables is proposed. These new models allow internal power losses of voltage source converters to be considered, leading to increased accuracy. The IEEE 14-bus system is used to illustrate and compare the main features of the proposed models.

Cascaded H-Bridge Voltage Reinjection—Part I: A New Concept in Multilevel Voltage–Source Conversion

A new multilevel configuration is proposed for use in voltage source conversion of large power and voltage ratings; it consists of the standard double bridge converter and a series chain of H-bridges, each connected to a capacitor. The H-bridge chain is connected between the middle node of the dc capacitors and the neutral point of the two main bridges. The new reinjection configuration provides all the features of the previously proposed multilevel reinjection schemes with a considerably reduced number of switches (that only increases in direct proportion to the converter dc voltage rating) and acts as a dynamic voltage balancer for the main bridge switches. Extensive simulation is carried out to verify the steady state waveforms and the dynamic behavior with reference to the STATCOM application.

Cascaded H-Bridge Voltage Reinjection—Part II: Application to HVDC Transmission

A three-phase converter configuration, with each phase consisting of a series chain of H-bridges has become a popular multilevel solution for STATCOM application. Such a configuration, however, is not suitable for HVDC transmission. A new concept, where the series chain of H-bridge cells is used to derive a multilevel voltage reinjection waveform, is described in a companion paper. Its application to HVDC transmission is discussed in this paper and extensive use is made of EMTDC simulation to verify its steady-state and dynamic behavior.

Two-Leg Three-Phase Inverter Control for STATCOM and SSSC Applications

Flexible ac transmission systems (FACTS) devices are attracting an increasing interest both in power system academic research and in electric utilities for their capabilities to improve steady-state performance as well as system stability. Several converter topologies for FACTS applications have been proposed in the recent literature, even if those based upon voltage source inverters (VSI) seem to be more attractive due to their intrinsic capability to rapidly respond to network changes such as perturbations subsequent to a fault and their property of being immune to resonance problem. In this paper, a new topology for inverter-based FACTS is proposed. This configuration, employing a two-leg three-phase inverter is employed for both series and parallel-connected reactive power compensators. The converter utilizes a modular topology for allowing a satisfaction of electronic components rating. A control strategy based on variable structure control technique with sliding mode is employed to track appropriate reference quantities. Design and control, as well as good tracking performances, are also verified through numerical simulations.

Unified power flow controller (UPFC) based on chopper stabilized diode-clamped multilevel converters

As the diode-clamped, multilevel converter has been found to have attractive features for STATCOM application, there is interest in extending it to UPFC application by using multilevel converters as the series and the shunt converters. Unfortunately, as is demonstrated in this paper, the DC voltages at their DC links, are inherently unstable. Faced with this impasse, a solution is sought in a system of local feedback controlled Class B choppers to equalize the DC. A laboratory experimental model establishes the feasibility of the proposal. Digital simulations show that current ratings in the choppers need be only 10% of the current ratings in the converters. The chopper cost is estimated as 1% of the cost of the multilevel converters.