Converter-based Static Synchronous Compensator Research Articles

Enhanced modular multi-level converter-based static synchronous compensator with social ski-driver optimized adaptive neuro-fuzzy inference system controller for power quality enhancement

Enhanced modular multi-level converter-based static synchronous compensator with social ski-driver optimized adaptive neuro-fuzzy inference system controller for power quality enhancement

Virtual Inertia Control for CHB-STATCOM in a Power Electronics Dominated Grid

Integration of renewable energy sources (RESs) leads the power system to be a low inertia system, resulting in frequency deviation in the grid. This paper presents a cascaded H-bridge (CHB) converter-based static synchronous compensator (STATCOM) providing virtual synchronous inertial support. This topology achieves two functionalities. 1. It reduces the system frequency deviation in a power electronics dominated grid (PEDG) following the updated grid codes. 2. Without disturbing the normal operation of CHB-STATCOM, it provides reactive power support. This topology uses the cumulative stored energy in the distributed DC-bus capacitors of CHB-STATCOM to improve the frequency nadir/zenith and the rate of change of frequency (RoCoF), preventing frequency instability. A closed- loop control algorithm is developed, which injects an adequate amount of stored energy to prevent frequency variation. It also facilitates re-energizing the capacitors in a smooth fashion, so that subsequent frequency events can be taken care of. For this, a high-pass-filter (HPF) is designed for autonomous DC- link voltage restoration for CHB converter. Relationship between frequency variation and inertial energy support by CHB is analyzed in depth. Finally, the viability of the proposed theory is verified in OPAL-RT test bench for step-up and step-down load change.

A Novel Fault-Tolerant Operation Approach for the Modular Multilevel Converter-Based STATCOM With the Enhanced Operation Capability

The operation capability of the modular multilevel converter (MMC)-based static synchronous compensator (STATCOM) is limited under submodule (SM) failures. When running in the STATCOM mode, the floating dc-link voltage of the MMC is adjustable. Therefore, this article proposes a novel fault-tolerant operation approach to enhance the operation capability of the MMC under severe SM failures. First, the dc-link voltage is dynamically regulated under SM failures, where the capacitor voltages of all SMs are slightly increased. The modulation ranges of the faulty and healthy phases can be enlarged, and the even voltage stress distribution can be realized. Then, a low-magnitude fundamental frequency zero-sequence voltage (FF-ZSV) is injected to balance the line-to-line voltages. Finally, the virtual energy idea is proposed, where the capacitor voltages of faulty SMs are considered to be clamped at the reference value. As a result, the arm energy reference will be the same in all six arms, and the arm energy balancing control is simplified. Detailed comparisons show that the proposed approach has an enhanced operation capability with lower capacitor voltage increment. Simulation and experimental results verify that even under severe SM failures, the proposed approach can still guarantee the fault-tolerant operation within the specified security region.

Modulated Model Predictive Control With Branch and Band Scheme for Unbalanced Load Compensation by MMCC-STATCOM

This article presents a novel modulated model-predictive control (MMPC) scheme for modular multilevel cascaded converter-based static synchronous compensator (STATCOMs) (MMCC-STATCOMs) to compensate unbalanced load current and regulate reactive power flow. By adding a common-mode voltage (CMV) to the phase-voltages of the star-connected MMCC current model, the method allows natural injection of a nonsinusoidal voltage to the neutral point of the converter, hence achieving interphase cluster voltage balance. Moreover, the imposed CMV is shown to extend the operating ranges of MMCC-STATCOMs when used for negative sequence current compensation. The proposed MMPC method incorporates a modified branch and bound algorithm to optimize the per-phase switch duty ratios. It is shown to be computationally more efficient compared to model-predictive control schemes using the optimal voltage level method combined with voltage sorting schemes. Experimental results with different weighting factors confirm the effectiveness of this control scheme and compared favorably with the conventional scheme of injecting only a sinusoidal zero-sequence voltage.

Modulated Model Predictive Control for Multilevel Cascaded H-Bridge Converter-Based Static Synchronous Compensator

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 (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PC) 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α–β</i> 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 M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PC method.

Wear-out failure analysis of modular multilevel converter-based STATCOM: The role of the modulation strategy and IGBT blocking voltage

The modular multilevel converter (MMC) is an attractive option for medium- and high-voltage static synchronous compensator (STATCOM) application. For this application, three aspects are relevant. Firstly, reliability and efficiency are directly related to the operation costs of this converter. Secondly, either high IGBT blocking voltage capability, featuring few number of submodules (SMs), or low-voltage IGBT modules, with a larger number of SMs, can be employed in an MMC-STATCOM. Lastly, either modulation strategies with fixed or variable switching frequency can be employed. Nevertheless, the literature does not present works evaluating these three aspects of an MMC-STATCOM at the same time. Therefore, this paper analyzes the impact of modulation strategies and number of SMs on wear-out failure and efficiency of an MMC-STATCOM. The effect of all SM components is considered. Two distinct modulation strategies are selected: phase-shifted pulse-width modulation (PS-PWM), with fixed switching frequency, and nearest-level control with cell tolerance band algorithm (NLC-CTB), with variable switching frequency. Four commercially available semiconductor blocking voltages are considered to evaluate the converter with different number of SMs. The results demonstrate that the number of SMs and the modulation strategy affect the MMC-STATCOM performance. Indeed, the converter presents different reliability at system-level and energy losses per year, depending on the IGBT blocking voltage and modulation strategy. The design with higher IGBT blocking voltage is the most affected.

Enhancement of Power Quality in an Actual Hot Rolling Mill Plant Through a STATCOM

A strategic use of a static synchronous compensator (STATCOM) for providing dynamic reactive power management of a hot rolling mill plant along with active mitigation of harmonics is considered in this article. More specifically, the behavior of a cascaded H-bridge (CHB) converter-based STATCOM is assessed. The impact of the steel to be milled and the specific features of the plant on the design of the STATCOM is discussed. The proposed strategy is analyzed from the point of view of reactive power flow management, active power loss reduction, and voltage control at the coupling point, as well as harmonics reduction and decrease of unscheduled shutdowns in the event of a trip in the passive filtering system. The article is based on real plant measurements, simulation tests, and results from an experimental platform built at scale, and represents the first stage of an ambitious plan to renew this type of plants aimed at transforming them into active elements for electrical energy management.

DC Capacitor Voltage Balancing Control for Delta-Connected Cascaded H-Bridge STATCOM Considering Unbalanced Grid and Load Conditions

In this paper, a comprehensive control scheme for a delta-connected cascaded H-bridge (CHB) converter-based static synchronous compensator (STATCOM) is presented, especially focusing on improving dynamic performance by novel feedforward control method. The method can conspicuously improve the dynamics of zero-sequence circulating current regulation of delta-connected CHB STATCOM especially under grid fault condition as well as load unbalance without excessive dc cell capacitor voltage fluctuation. The validity of the proposed method is demonstrated by mathematical proof. Finally, the full-scaled simulation results and the down-scaled experimental results verify that stable operation is guaranteed for both emulated grid and load unbalance conditions.

Performance investigation of nine-level cascaded H-bridge inverter-based STATCOM for mitigation of various power quality problems

This paper deals with the design and implementation of cascaded H-bridge multilevel voltage source converter-based static synchronous compensator (STATCOM) for simultaneous active and reactive power compensation, voltage stability and damping of power oscillations. The main objective is to provide active power support and maintain the voltage stability by compensating the reactive power in the power system. In this paper, the multi pulse inverter-based STATCOM has been replaced by multilevel inverter-based STATCOM to overcome the drawbacks of the former. Cascaded H-bridge (CHB) MLI for implementation of STATCOM has been used as CHB MLI is considered the best for STATCOM applications due to its modular structure and requirement of lesser number of components. MLI-based STATCOM is used to provide simultaneous reactive power and active power compensation established by using super-capacitor. The super-capacitors are connected with each DC link capacitor of CHB MLI by using the DC-DC buck boost converter. The STATCOM is also used to provide voltage stability during the power quality problems such as voltage sag and voltage swell, it is established by injecting or absorbing reactive power. The STATCOM is also used for damping the power oscillations by controlled injection of reactive power hence enhancing transient stability. Nine-level cascaded H-bridge MLI-based STATCOM is designed for simultaneous reactive power and active power compensation, voltage stability and damping the power oscillations. Exhaustive simulations have been carried out using MATLAB/Simulink and SimPowerSystems software. The simulation results are presented to prove the effectiveness of MLI-based STATCOM for simultaneous active and reactive power compensation, voltage stability and damping of power oscillation.

Fixed-time dynamic surface high-order sliding mode control for chaotic oscillation in power system

In this paper, a fixed-time dynamic surface high-order sliding mode control approach is presented for chaos suppression and voltage stabilization in three-bus power system via design of current source converter-based static synchronous compensator controller. The proposed control strategy constructs two high-order sliding mode surfaces to achieve control objective. By combining backstepping idea with dynamic surface control (DSC) technique, high-order sliding mode controller is designed and the inherent problem of “explosion of complexity” in backstepping design is avoided. Further, a new stability concept is introduced into DSC design to achieve semi-global uniform ultimate boundedness of the signals in high-order sliding mode system within finite time independent of initial condition. In addition, stability analysis is provided to show that the proposed control scheme can achieve semi-globally fixed-timely uniformly ultimately bounded stabilization. Finally, simulation results are given to demonstrate the effectiveness of the proposed control scheme and the superior performance over conventional DSC.

Reduced-Capacitance Thin-Film H-Bridge Multilevel STATCOM Control Utilizing an Analytic Filtering Scheme

In this paper, an analytic capacitor voltage filtering scheme for a cascaded H-bridge (CHB) multilevel converter-based static synchronous compensator (STATCOM) is proposed. The scheme is able to filter out a low-frequency ripple of any magnitude and introduces a negligible delay to the control system. Therefore, it facilitates using high-reliability film capacitors with low capacitance instead of the conventional electrolytic capacitors. The proposed analytic filtering scheme is implemented and verified on a single-phase seven-level CHB multilevel converter-based STATCOM. The parameters' sensitivity evaluation is provided to demonstrate practicability of the proposed scheme. Simulation and experimental results are provided to compare the performance of the proposed filtering scheme with the performance of the most commonly used second-order filter-based approach to demonstrate its effectiveness.

Indirect Matrix Converter-Based Topology and Modulation Schemes for Enhancing Input Reactive Power Capability

A new topology based on indirect matrix converter (IMC) is proposed to enhance the input reactive power capability. This topology consists of a conventional IMC and an auxiliary switching network (ASN), which is connected to the dc-link of the IMC in parallel. With the aid of ASN, an implicit current source converter-based static synchronous compensator can be embedded into an IMC, which lays a foundation for the input reactive power control. Based on the proposed topology, two modulation schemes are presented, and the formations of the output voltage and input reactive current are decoupled in both of them. To minimize power loss and improve input current quality, a double closed-loop control algorithm is introduced, in which the current through the dc inductor in ASN is controlled to be minimum. Different from the conventional IMC, the input reactive power of the topology is independent of its load condition without considering the practical constraints. The effectiveness of the proposed topology and modulation scheme is confirmed by experimental results.

STATCOM analysis of twin converter using PWM technique

This paper addresses a two different configuration of shunt connected static synchronous compensator (STATCOM) namely a six pulse voltage source converter-based static synchronous compensator (STATCOM) and a 12 pulse voltage source converter-based static synchronous compensator with two different dc link voltages to demonstrate its effectiveness in maintaining stability of the voltage in a 600 km transmission line. The main objective of this paper is to maintain simple and fast voltage regulation at any point in the transmission line with reduce total harmonic distortion (THD) by connecting the twin converter-based static synchronous compensator to the grid through accomplishing indirect current control (ICC) technique which in turn utilities four PI control loops. The indirect current controller is developed to produce the modulation signals in order to generate the gate signals for the two voltage source converters (VSCs) by using the phase shifted carrier-based pulse width modulation (PWM) topology. Here simulation studies is performed with the above mentioned static synchronous compensator configurations and finally concludes that twin converter-based static synchronous compensator operates satisfactorily under power quality problems such as voltage interruption, sag, etc. compared to conventional static synchronous compensator.

High-Power VSC-Based Simultaneous Positive- and Negative-Sequence Voltage Regulator

A voltage-source converter-based static synchronous compensator (STATCOM) is used in transmission and distribution systems for the purpose of voltage regulation and reactive power compensation. In the transmission level, angle-controlled STATCOMs are of primary interest due to their high efficiency and excellent waveform quality. There is a considerable number of angle-controlled STATCOMs installed in the different utilities in the U.S. Despite the high efficiency and good voltage quality, this type of STATCOM shows poor performance under ac system faults. They are usually tripped under severe unbalanced condition and system faults to protect the switches from huge negative-sequence current flow. This paper provides a solution to improve the transmission-level STATCOM performance under power system faults. The proposed solution is based on adding a single-phase inverter in series with the converter dc bus. One specific controller is designed which provides the capability of simultaneously controlling positive- and negative-sequence voltages. The results are supported by detailed simulation studies on the New York Power Authority STATCOM model using PSCAD/EMTDC.

Two-level 24-pulse double-way voltage source converter-based STATCOM

This paper presents a two-level 24-pulse double-way voltage source converters (VSCs) configuration for the static synchronous compensator (STATCOM). It uses four identical six-pulse double-way VSC sets to form a 24-pulse VSC configuration of STATCOM. Each six-pulse double-way VSC set consists of two sets of two-level three-phase six-pulse gate turn off thyristor (GTO) VSCs. The phase angle difference between the fundamental ac voltages of two three-phase six-pulse GTO VSCs is varied for the reactive power control. The STATCOM is operated at a constant dc link voltage which results in better utilisation of the converter compared to the operation of the STATCOM with variable dc link voltage. The STATCOM is designed for ±100 MVAR and connected to a 33 kV/60 Hz ac system to evaluate its performance by varying the reference reactive power. The model of proposed STATCOM is developed using MATLAB along with Simulink, sim-power system (SPS) toolboxes and simulation results demonstrate its satisfactory steady state and dynamic performances.