Control Strategy Of Static Synchronous Compensator Research Articles

Wideband Harmonic Voltage Feedforward Control Strategy of STATCOM for Mitigating Subsynchronous Resonance in Wind Farm Connected to Weak Grid and LCC HVDC

For the wind farm connected to line-commutated converter-based high-voltage direct-current (LCC HVDC) and weak grid at sending end, subsynchronous resonance (SSR) is prone to occur due to the impedance interactions among wind farm, weak grid, and LCC HVDC. First, the mechanism and characteristics of this SSR are analyzed based on the impedance method. With the increase of the output power for wind farm or the decrease of the transmission power for LCC HVDC, the wind farm tends to cause SSR. Moreover, with the decline of the grid stiffness at sending end, the studied system easily causes SSR. Then, a wideband harmonic voltage feedforward control strategy of static synchronous compensator (STATCOM) is proposed to suppress this SSR. For the proposed damping controller of SSR, a constant voltage amplitude-based harmonic extraction method is designed without using filter. The harmonic extraction error of the proposed strategy is a constant |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> |, which is induced by the difference between the constant voltage amplitude V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> and actual voltage amplitude V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> . By the theoretical analysis and simulation, this constant error |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> | can be automatically counteracted by the PI controller of STATCOM. Finally, experimental results verify the validity of the proposed strategy.

Research on Control Strategy of STATCOM for Suppressing Subsynchronous Oscillation Based on Nonlinear Method

The dq-axis’ current is flowing into the static synchronous compensator (STATCOM) from the power system and the dq-axis’ current reference value form an error signal. After processing the error signal, a trigger pulse is formed to control the turn-on and turn-off of thyristors in STATCOM. At present, various documents generally adopt PI control to process the error signal. But the coefficient of PI control is difficult to set and the response speed of STATCOM under this control is not very satisfactory. In the paper, a STATCOM control strategy based on nonlinear method is proposed. By introducing feedback controlled quantities u 1(t) and u 2(t) into item piq and pid of the STATCOM mathematical model after dq transformation, the aim is to actively control the AC and DC axis current components of STATCOM input system. Based on the principle of nonlinearity, a set of multi-input and multi-output objective functions y 1 and y 2 are found. The dynamic and static performance of the control target is dynamically tracked and constrained by the secondary performance index, thus a closed-loop control system is formed which can quickly reflect the varying reactive power of the system. Finally, PSCAD/EMTDC electromagnetic transient simulation software is used to verify the effectiveness of the STATCOM nonlinear control method of Suppressing sub-synchronous oscillation in power system.

Modified STATCOM control strategy for fault ride-through capability enhancement of grid-connected PV/wind hybrid power system during voltage sag

This paper proposes the employment of Static Synchronous Compensator (STATCOM) in reactive power compensation to enhance the Fault Ride-Through (FRT) capability and improve the dynamic performance of a grid-connected PV/wind hybrid power system during the transient grid disturbances. The hybrid power system consisting of 9 MW Doubly Fed Induction Generator (DFIG)-based wind farm and 1 MW PV station is integrated with 100 MVAR STATCOM at the Point of Common Coupling (PCC) bus. The dynamic performance of the PV/wind hybrid power system with the proposed STATCOM controller is analyzed and compared with another FRT control strategy during a grid voltage sag. The FRT control strategy is based on the injection of reactive power from the hybrid system to enhance the FRT capability during the grid faults, and also activation of the outer crowbar protection system to protect the DFIG. On the other hand, the proposed STATCOM controller adjusts the PCC bus voltage during the grid disturbances by dynamically controlling the amount of reactive power injected to or absorbed from the electrical grid. Modeling and simulation of the proposed hybrid power system have been implemented using MATLAB/SIMULINK software. The effectiveness of both the proposed STATCOM controller and the FRT control strategy is evaluated during a 50% grid voltage sag. The simulation results illustrate that the STATCOM controller decreases significantly the level of voltage drop during the voltage sag, maintains the injected active power from the PV station at its rated value, and protects effectively the PV DC-link voltage from overvoltage. Moreover, when the STATCOM controller is employed, the injected active power from the wind farm is improved considerably and the oscillations of the DFIG rotor speed are reduced efficiently during the fault. Furthermore, the comparison confirms the superior dynamic performance of the STATCOM controller in enhancement the FRT capability as compared with the FRT control strategy.

Improved Coordinated Control Strategy for Hybrid STATCOM Using Required Reactive Power Estimation Method

The penetration level of renewable energy resources has grown in such a way that their effects on the power system can no longer be neglected. In order to cope with these problems, grid operators are forced to improve the stability of the grid connection point, and the static synchronous compensator (STATCOM), which has a fast dynamic response is emerging as an alternative. Due to the prohibitive cost of STATCOM, however, grid operators have begun applying a new concept of hybrid STATCOM, which is a combination of mechanically switched capacitors (MSCs) and STATCOM. Thus, this paper investigates the use of new coordinated control between STATCOM and MSCs, and the solution relies on the required reactive power estimation method using online grid strength level (OGSL) index, which is newly proposed in this paper, and the optimal MSCs allocation algorithm. Following the proposed procedure, an improved coordinated control scheme is obtained whose objective is to reduce the switching times of the MSCs while maximizing the reserve reactive power margin of the STATCOM in transient state. This proposal is analyzed on the Jeju island power system in South Korea with the developed hybrid STATCOM model.

Nonlinear coordinated control of STATCOM and generator excitation for multi‐machine power systems based on improved multi‐objective holographic feedback

Aiming at the coordination control problem of the static synchronous compensator (STATCOM) and generator excitation in a multi‐machine system, an improved multi‐objective holographic feedback (IMOHF) control method is proposed to ensure good dynamic and static state performance of each state in the system. First, the essence of IMOHF is deduced by the Hartman–Grobman theorem. The nonlinear differential algebraic equation (NDAE) system is used to arrange the poles in the vicinity of the equilibrium point by nonlinear feedback; the feedback coefficients are adjusted to constrain the objective variables, so that the variables converge rapidly in their respective references. Then this design concept is applied to the decentralized coordination control strategy of STATCOM and generator excitation. Two kinds of multi‐objective holographic feedback nonlinear control laws with active power, synchronous speed, generator terminal voltage, and STATCOM terminal voltage as control objectives are obtained. Simulation result of the three‐machine nine‐bus system shows that these two kinds of control laws can effectively restrain the power system oscillation and improve the transient stability of the system, and consequently the system voltage will not generate any static shift under different disturbances. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

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.

Power Quality Improvement and LVRT Capability Enhancement of Wind Farms by Means of an Inductive Filtering Method

Unlike the traditional method for power quality improvement and low-voltage ride through (LVRT) capability enhancement of wind farms, this paper proposes a new wind power integrated system by means of an inductive filtering method, especially if it contains a grid-connected transformer, a static synchronous compensator (STATCOM) and fully-tuned (FT) branches. First, the main circuit topology of the new wind power integrated system is presented. Then, the mathematical model is established to reveal the mechanism of harmonic suppression and the reactive compensation of the proposed wind power integrated system, and then the realization conditions of the inductive filtering method is obtained. Further, the control strategy of STATCOM is introduced. Based on the measured data for a real wind farm, the simulation studies are carried out to illustrate the performance of the proposed new wind power integrated system. The results indicate that the new system can not only enhance the LVRT capability of wind farms, but also prevent harmonic components flowing into the primary (grid) winding of the grid-connected transformer. Moreover, since the new method can compensate for reactive power in a wind farm, the power factor at the grid side can be improved effectively.

Research on Improved Control Strategy for STATCOM Based on Virtual Matrix Method

Fast and accurate detection of reactive current is the precondition for the realization of static synchronous compensator (STATCOM) reactive power compensation and harmonic suppression. Aiming at deviation and delay of the traditional reactive current detection algorithm with phase-locked loop (PLL) and low-pass filter (LPF) of STATCOM, a novel improved reactive current detection algorithm without PLL is proposed, in which the virtual matrix (VM) is built to replace the original PLL, and improved current average value filter is used to realize the function of LPF, so as to improve the real-time performance and robustness of reactive current detection. The realization process of VM detection method is derived in this paper, and improved control strategy for STATCOM is designed based on the VM detection method. Simulation analysis of the proposed detection algorithm and control strategy is conducted in Matlab platform so as to verify the correctness and effectiveness of the control strategy. The VM detection has the advantages of simple structure, fast response and easy for digital realization, which provides reference for the improvement of reactive power compensation precision for STATCOM.

Development of optimal shunt hybrid compensator based on improving the measurement of various signals

Voltage and current harmonics generated by nonlinear loads in power systems cause a reduction in electric power quality (EPQ) which has recently become a serious preoccupation in electrical networks due to the increasing number of perturbing loads such as electric arc furnaces and nonlinear loads. Various devices such as static Var compensator (SVC) and static synchronous compensator (STATCOM) can be used to improve EPQ. Due to economic issues, using a STATCOM with high-rated power is not cost-effective. So, development of hybrid compensator based on STATCOM and SVC, type of TCR-BPF, is proposed in this paper by improving the measurement of various signals in their control systems. Hence, the SVC will compensate the fundamental reactive power and balancing of nonlinear load and STATCOM can be used with lower-rated power as an active filter to eliminate the harmonics generated by set of TCR and load. Also, STATCOM compensates the reactive power, voltage flicker, and the unbalancing load which SVC has not been able to compensate them. To use all of the capabilities of TCR-BFP, its control system is improved by new TCR reactive power measurement and predicted reactive power (PRP). Also, the STATCOM control strategy is optimized by FPSO method. Then, the proposed hybrid compensator is implemented in one of the largest steel industries in Iran, Mobarakeh Steel Company (MSC).

三电平STATCOM新型直接功率控制策略研究

三电平静止同步补偿器(STATCOM)在配电网无功补偿领域发挥重要的作用。在三电平STATCOM控制策略中，传统的滞环式直接功率控制策略具有开关频率不固定的缺陷，这为网侧滤波器的设计带来了困难。本文提出一种新型三电平STATCOM定频直接功率控制策略。该策略从三电平STATCOM数学模型出发，以三电平SVPWM策略作为调制策略，采用以PI控制器为核心的前馈解耦控制系统对瞬时功率进行控制，以直流总电压的平方项为外环控制目标，在实现系统开关频率固定的同时得到良好的无功补偿效果。最后通过仿真验证了本文提出方法的正确性和合理性。 The three-level STATCOM (static synchronous compensator) plays an important role in the reactive power compensation of the distribution system. In all of the control strategies of three-level STATCOM, traditional hysteresis direct power control (DPC) strategy has the characteristics of uncertain switching frequency which made the grid connected filter hard to design. In this paper, it presents a novel constant switching frequency direct power control strategy of three-level STATCOM. The novel strategy based on the mathematical model of three-level STATCOM, and three-level SVPWM strategy is used as modulation strategy. Using PI controller and instantaneous power feedforward and decoupling control, the novel strategy realizes constant switching frequency as while as good reactive compensation effect. Finally, the simulation verified the correctness and rationality of the proposed method.

Enhanced fault ride through performance of self‐excited induction generator‐based wind park during unbalanced grid operation

This study presents novel control design for improving the performance of large-scale wind park (LSWP) based on self-excited induction generator under unbalanced voltage conditions. A dual controller for static synchronous compensator (STATCOM) employing controller by employing positive- and negative-sequence synchronous frames is implemented and analysed in response to severely unbalanced voltage conditions. The test system simulated represents a wind park rated at 100 MW connected to a weak electrical grid. The potential of the dual STATCOM controller is evaluated and analysed for severely unbalanced voltage conditions at the grid interface of LSWP. The dual controller with STATCOM overloading capability is tested and compared with the performance of the positive-sequence controller in response to different types of asymmetrical grid faults at low short-circuit ratios. The simulations performed using PSCAD/EMTDC demonstrate superior performance of dual STATCOM control strategy for improving unbalanced operation, fault ride through capability and transient stability margin in response to severely unbalanced voltage conditions.

A Novel Control Strategy for Three-Phase Four-Wire STATCOM

Nowadays Static Synchronous Compensator (STATCOM) has gradually become one of the representative techniques in the field of dynamic reactive power compensation in the power distribution system. This paper analyzed the topology and the voltage imbalance problem of the up and down capacitors on DC side of the three-phase four-wire STATCOM. In allusion to the imbalance problem of neutral point, a novel control strategy based on the control of zero-sequence current was proposed. By the triple close-loop control strategy, the STATCOM can achieve great control accuracy and dynamic performance. Simulation result proves that the proposed control method is effective.

STATCOM Stabilizer based on Fuzzy Logic Control for Damping Power Oscillation

Problem statement: In power systems, there exists a continuous challenge to improve dynamic performance of power system. Approach: Static Synchronous Compensator (STATCOM) is a power electronic based device that has the capability of controlling the power flow through a line. This study applies the Static Synchronous Compensator (STATCOM) to control the power flow during dynamic period. To verify the effect of the STATCOM on dynamic performance, the mathematical model and control strategy of a STATCOM was needed to be presented. The converters of STATCOM were represented by variable voltage source with associate transformer leakage reactance and the voltage source and the reactance were transformed into current injection. The current injection model of STATCOM was modeled into power flow equation and thus it was used to determine control strategy. This study applies the fuzzy logic control to determine the control strategy of STATCOM. The swing curves of the three phase faulted power system without and with a STATCOM was tested and compared in various cases. Results: The swing curve of the system with STATCOM based fuzzy logic control had the less amplitude during the dynamic period. Conclusion: STATCOM can improve the dynamic performance of the system after disturbance.

STATCOM Impact Study on the Integration of a Large Wind Farm into a Weak Loop Power System

Recently, renewable wind energy is enjoying a rapid growth globally to become an important green electricity source to replace polluting and exhausting fossil fuel. However, with wind being an uncontrollable resource and the nature of distributed wind induction generators, integrating a large-scale wind-farm into a power system poses challenges, particularly in a weak power system. In the paper, the impact of static synchronous compensator (STATCOM) to facilitate the integration of a large wind farm (WF) into a weak power system is studied. First, an actual weak power system with two nearby large WFs is introduced. Based on the field SCADA data analysis, the power quality issues are highlighted and a centralized STATCOM is proposed to solve them, particularly the short-term (seconds to minutes) voltage fluctuations. Second, a model of the system, WF, and STATCOM for steady state and dynamic impact study is presented, and the model is validated by comparing with the actual field data. Using simulated PV and QV curves, voltage control and stability issues are analyzed, and the size and location of STATCOM are assessed. Finally, a STATCOM control strategy for voltage fluctuation suppression is presented and dynamic simulations verify the performance of proposed STATCOM and its control strategy.

Evaluation of Cascade-Multilevel-Converter-Based STATCOM for Arc Furnace Flicker Mitigation

As an industry customer of electric power, an electrical arc furnace (EAF) is a major flicker source that causes major power quality problems. For a 40-MVA EAF in Tennessee, USA, a cascade-multilevel converter (CMC)-based STATic synchronous COMpensator (STATCOM) with high bandwidth is proposed for EAF flicker mitigation. In this paper, flicker mitigation techniques by using a CMC-based STATCOM are presented and verified through a transient network analyzer (TNA) system. The required STATCOM capacity is first studied through a generalized steady-state analysis. Second, the STATCOM control strategy for flicker mitigation is introduced, and simulation results are given. Finally, a TNA system of the STATCOM and an EAF system are designed and implemented. Experimental results from the TNA test show that the proposed CMC-based STATCOM and its controller can efficiently and rapidly mitigate the EAF flicker

Stabilization of Wind Turbine Generator System by STATCOM

Recently voltage-source or current-source inverter based various FACTS devices have been used for flexible power flow control, secure loading, damping of power system oscillation and even for the stabilization of wind energy generation. In this paper, we propose the static synchronous compensator (STATCOM) based on voltage source converter (VSC) PWM technique to stabilize grid connected wind generator system. A simple control strategy of STATCOM is adopted where only measurement of rms voltage at the wind generator terminal is needed. Fuzzy logic controller rather than conventional PI controller is proposed as the control methodology of STATCOM. Multi-mass shaft model of wind turbine generator system (WTGS) is also considered as shaft modeling has a big influence on the transient performance of WTGS. Transient performance of STATCOM connected WTGS is compared also with that of pitch controlled WTGS. Both symmetrical and unsymmetrical faults are analyzed. Moreover, the steady state performance of STATCOM connected WTGS is analyzed. It is reported that STATCOM can reduce the voltage fluctuation significantly. Finally STATCOM is applied to a wind park model with multiple wind generators. Comprehensive results are presented to assess the performance of STATCOM connected WTGS, where the simulations have been done by PSCAD/EMTDC.