Small Signal Disturbances Research Articles

Research on impedance measurement based on Gallium Nitride Transistor

Abstract Impedance measurement has broad applications in fields such as electrochemistry, biology, medicine, and food safety. Typically, frequency response analyzers are used for small signal disturbance measurements, but they come with drawbacks such as high cost, large size, and limited excitation capabilities. To address the need for wide-band, large-signal, and portable impedance measurement in electrochemical applications, a novel scheme based on a Gallium Nitride device excitation circuit and amplitude-phase discrimination module is proposed. A multiphase cascade frequency-doubling buck circuit is used to inject disturbance signals into the impedance under test, and impedance parameters are obtained using discrete fourier transformafter signal sampling. By varying the frequency of the disturbance signal, impedance information across different frequencies can be captured. In this approach, the amplitude-phase discrimination module replaces the frequency response analyzer, reducing the overall size of the measurement system, while the power device-based excitation circuit enables large signal disturbances.

Augmented Two-Stage Hierarchical Controller for Distributed Power Generation System Powered by Renewable Energy: Development and Performance Analysis

The sustainable development of an area is highly reliant on a reliable electrical energy supply. Microgrids are important in integrating distributed energy resources (DERs) using power electronic converters. However, microgrid control becomes challenging with the increasing number of distributed generators and loads. With the conventional droop control method, power contributions from DER converters cannot be accurately shared due to a mismatch of line impedances. In this paper, an augmented hierarchical control mechanism is proposed to solve the issues mentioned above. This hierarchical control mechanism consists of primary and secondary controllers. The primary stage utilized the droop controller to improve optimal power flow, mainly for the resistive network. The secondary stage is based on an improved methodology to compensate for the voltage and frequency variations during small and large signal disturbances. Moreover, the modelling and analysis for PMSG-based wind energy conversion systems are also presented. The response of the primary controller for active and reactive power sharing is investigated. The analysis emphasizes the demonstration of optimal power-sharing under normal and abnormal conditions for the considered load. Finally, the suggested robust controller’s performance is evaluated in a MATLAB environment, and simulation results show the proposed scheme’s superiority under different operating conditions. The frequency is stable at 50 Hz after a 50 KW load is added.

Large-Signal Stability Analysis of DC Distribution Systems With Cascading Converter Structure

DC-DC converters are major components of the DC distribution systems. The converters interface with external power inputs, internal DC buses and loadings of subsystems. The interfacing DC-DC converters should be stable locally and globally under mutual interactions through a DC bus within the system. Current research efforts have focused on the analysis of the stability of the DC distribution system subject to small-signal disturbance. However, in practice, the system routinely operates under large-signal disturbances, such as when an additional subsystem is turned on after being connected to the DC bus. In this scenario, the small-signal model may fail to fully describe the dynamics of the system. In this paper, we identify and analyze the bifurcation process when the system undergoes abrupt load changes. According to the nonlinear operation of the interconnected system, a large-signal stability criterion is derived. This criterion is simple, and can be easily extended to multiple connected converter systems. The criterion is also consistent with the result from bifurcation analysis. Finally, the validity of the proposed criterion is verified by the full-circuit simulations and the experimental works.

Utilisation of synchronous condensers for improved damping in power systems with high renewable penetration

With ever increasing variable renewable energy (VRE) and subsequent displacement of conventional synchronous generation (CSG), system strength and inertia have been steadily declining in power system grids around the world. A mitigation to the aforementioned problem is installation and operation of synchronous condensers (SC) for provision of system strength and inertia. While the synchronous condenser is a mature and proven technology, the technology has not been fully utilised, particularly in its ability to provide additional damping to system inter-area modes via Power Oscillation Damper (POD) controllers. Synchronous condensers can provide inertia and modulation of terminal reactive power and voltage (via the excitation system) to impact the system power flows such that it can provide a positive contribution to system damping. This paper examines the implementation of a synchronous condenser in conjunction with a POD, in a network with high renewable generation, to dampen inter-area modes. Firstly, we investigate a method to determine the ideal location and monitoring Bus of a synchronous condenser, for damping of inter-area modes. Subsequently, the inertia time constant and POD settings are optimised to provide adequate modulation of the SC terminal voltage and reactive power for increased damping of interarea modes. Finally, large and small-signal disturbances are considered with and without the POD to demonstrate the device effectiveness.

Inferring Power System Dynamics From Synchrophasor Data Using Gaussian Processes

Synchrophasor data provide unprecedented opportunities for inferring power system dynamics, such as estimating voltage angles, frequencies, and accelerations along with power injection at all buses. Aligned to this goal, this work puts forth a novel framework for learning dynamics after small-signal disturbances by leveraging Gaussian processes (GPs). We extend results on learning of a linear time-invariant system using GPs to the multi-input multi-output setup. This is accomplished by decomposing power system dynamics into a set of single-input single-output linear systems with narrow frequency pass bands. The proposed learning technique captures time derivatives in continuous time, accommodates data streams sampled at different rates, and can cope with missing data and heterogeneous levels of accuracy. While Kalman filter-based approaches require knowing all system inputs, the proposed framework handles readings of system inputs, outputs, their derivatives, and combinations thereof collected from an arbitrary subset of buses. Relying on minimal system information, it further provides uncertainty quantification in addition to point estimates of system dynamics. Numerical tests verify that this technique can infer dynamics at non-metered buses, impute and predict synchrophasors, and locate faults under linear and non-linear system models under ambient and fault disturbances.

Dynamics of Inverter-Based Resources in Weak Distribution Grids

This work presents the modelling fundamentals to study the dynamics of inverter-based resources (IBRs) in weak distribution grids and derive disturbance performance characteristics describing how they should behave under different conditions. More specifically, with respect to small-signal disturbances we study the possible voltage violations following frequency response from IBRs due to low system strength and also propose specific design requirements for IBR <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> current control to guarantee a stable response. In the context of large-signal disturbances, we highlight how active power-voltage control may not be effective due to a delay imposed by the physical features of the distribution network. Further, we mathematically discuss how IBR reactive power control could enhance its phase-locked loop stability. The proposed disturbance performance characteristics are then integrated into the IBR converter control via a novel voltage-priority reference generation strategy. Simulation results on a real Australian network show the efficacy of the proposed operational and control design requirements, and highlight possible unexpected active/reactive power interactions in weak distribution grids.

Impedance-Based Analysis and Stability Improvement of DFIG System Within PLL Bandwidth

In this article, we analyze the negative impact of phase-locked loop (PLL) on the stability of the doubly fed induction generators system. The small-signal disturbance of PLL mainly affects the coordinate transformation of the rotor current and introduces a negative resistance within PLL bandwidth. Two impedance reshaping methods are carried out to weaken this negative resistance. A virtual impedance in the conventional current control is added to the first reshaping method. The second reshaping method completely removes the coordinate transformation of the rotor current by switching the control target from current to power. The difference between these two reshaping methods is analyzed based on the equivalent single-input single-output impedance model. The experimental results validate the effectiveness of these two reshaping methods and the superiority of the second reshaping method at a lower short-circuit ratio.

Microsecond Enhanced Indirect Model Predictive Control for Dynamic Power Management in MMC Units

The multi-modular converter (MMC) technology is becoming the preferred option for the increased deployment of variable renewable energy sources (RES) into electrical power systems. MMC is known for its reliability and modularity. The fast adjustment of the MMC’s active/reactive powers, within a few milliseconds, constitutes a major research challenge. The solution to this challenge will allow accelerated integration of RES, without creating undesirable stability issues in the future power system. This paper presents a variant of model predictive control (MPC) for the grid-connected MMC. MPC is defined using a Laguerre function to reduce the computational burden. This is achieved by reducing the number of parameters of the MMC cost function. The feasibility and effectiveness of the proposed MPC is verified in the real-time digital simulations. Additionally, in this paper, a comparison between an accurate mathematical and real-time simulation (RSCAD) model of an MMC is given. The comparison is done on the level of small-signal disturbance and a Mean Absolute Error (MAE). In the MMC, active and reactive power controls, AC voltage control, output current control, and circulating current controls are implemented, both using PI and MPC controllers. The MPC’s performance is tested by the small and large disturbance in active and reactive powers, both in an offline and online simulation. In addition, a sensitivity study is performed for different variables of MPC in the offline simulation. Results obtained in the simulations show good correspondence between mathematical and real-time analytical models during the transient and steady-state conditions with low MAE. The results also indicate the superiority of the proposed MPC with the stable and fast active/reactive power support in real-time simulation.

A Dual-Layer Back-Stepping Control Method for Lyapunov Stability in Modular Multilevel Converter Based STATCOM

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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Lyapunov</i> 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.

A Fuzzy Adaptive PID Control Algorithm with Improved Quantification Factor

The phase-shifting full bridge digital power supply based on Fuzzy PID control is difficult to realize the full mapping from the fuzzy universe to the actual output domain, resulting in the loss of fuzzy control quantity, resulting in the dynamic performance problems of large amplitude and long time output fluctuation. In this paper, a fuzzy adaptive PID control algorithm with improved quantification factor is proposed. The online adjustment function of quantification factor in fuzzy universe is introduced in the quantification link. The function can adjust the fuzzy quantification factor in real time according to the current sampling error and error change rate of the system. In order to verify the effectiveness of the improved algorithm, the traditional PID control, the traditional fuzzy PID control and the quantification factor improved fuzzy PID control are applied to the phase-shifting full bridge small signal disturbance model respectively. The results show that the fuzzy adaptive PID control algorithm with the quantification factor online adjustment function has higher dynamic performance.

Intelligent Control Algorithm of Impulse Current for Two Stage Wide Input Marine Switching Power Supply

Wang, G. and Hu, Y., 2020. Intelligent control algorithm of impulse current for two stage wide input marine switching power supply. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 956–960. Coconut Creek (Florida), ISSN 0749-0208.In order to solve the problem of large ripple caused by high current pulse load in the operation of conventional ship power network, an intelligent control algorithm for shock current of two-stage wide input switching power supply for ships is proposed. Based on the variation law of disturbance period, the influence of frequency disturbance is analyzed, a steady-state large signal model is established, the small signal disturbance of switch frequency is calculated, the parallel current sharing technology is used to realize the parallel current sharing control of switch power supply, and the intelligent control algorithm of shock current of two-stage wide input ship switch power supply is completed. The experimental results show that, after using the proposed control algorithm, the secondary current and the primary current have a high degree of agreement, which indicates that it can effectively prevent the occurrence of excessive ripple caused by current pulse load.

Backstepping Control for Large Signal Stability of High Boost Ratio Interleaved Converter Interfaced DC Microgrids With Constant Power Loads

With the penetration of renewable generation and tightly regulated power electronic loads, the power quality and stability of modern dc microgrids are greatly challenged. To solve this problem, energy storage systems (ESSs) are widely proposed. Unfortunately, most of the existing control methods for ESSs can only ensure the stability of dc microgrids with small signal disturbances, which may not be satisfying for real-time applications where large signal disturbances exist. Moreover, they are usually designed for low boost ratio and low power converters, negating their suitability for grid-scale applications. To ensure the large signal stability of dc microgrids using high boost ratio interleaved converter interfaced ESSs, this article proposes a new backstepping control strategy with finite-time disturbance observers. Its effectiveness is verified by simulation and experiments carried out on an interleaved double dual boost converter.

Small-Signal Disturbance Compensation Control for LCL-Type Grid-Connected Converter in Weak Grid

When the three-phase LCL -type converter is attached to a weak grid, its grid current control will interact with a phase-locked loop (PLL), via the point of common coupling voltage. And, the PLL dynamic has a negative influence on the current control, rendering an undesired performance to grid current control, even leading to the instability issue, if no effective measure is employed. To mitigate this problem, this article proposes a simple and visualized small-signal disturbance compensation control method for the LCL -type grid-connected converter. First, the effect mechanism of PLL dynamic on the current control is analyzed, and the root of the small-signal disturbance caused by PLL dynamic is identified subsequently. Based on this, an improved control method is proposed to compensate the aforesaid PLL-introduced small-signal disturbance terms in current loop, and then, the negative effect of PLL dynamic on the grid current control can be effectively reduced in the weak grid, without modifying the PLL parameters and structure. Moreover, the method is not influenced by the circuit parameters change, and it is robust to the variation of grid impedance. Finally, the proposed method is validated by the experiment.

Stability analysis of integrated power system with pulse load

The stability of an integrated power system (IPS) with pulse load involves both the trend of change in the system state during the whole period and the problem of whether to cause an unacceptable oscillation and an increase or decrease in the system state variable during a pulse period, which will pose a great challenge to the IPS. This paper considers the system stability in two aspects: the stability of system state variables in a periodic steady state under the action of pulse load, which refers to the stability of the periodic orbit, and the problem mentioned above, which cannot be described according to the stability of the equilibrium point and so needs further research. The analysis of the first aspect can lay the foundation for a study of the second aspect. This paper presents a mathematical model of the IPS with pulse load, uses the periodic-orbit method to analyze the system stability and stable margin and drives a state space averaging model of the system. For a relatively small state variable disturbance of the system under small signal disturbance, the state-space averaging method proves to be approximate to the periodic-orbit method. On this basis, the conventional state-space averaging method can be used for the analysis of system stability. The simulation and calculation show that the proposed method is feasible and effective.

A Two-Level Hierarchical Controller to Enhance Stability and Dynamic Performance of Islanded Inverter-Based Microgrids With Static and Dynamic Loads

This paper proposes phasor measurement unit (PMU) supported two-level hierarchical controller to enhance stability and dynamic performance of islanded inverter-based microgrids with static and dynamic loads. The proposed hierarchical controller consists of a local decentralized controller for each inverter-interfaced distributed generation (IIDG) unit at the primary level helped by a multi-input multioutput centralized controller at the secondary level. The primary-level decentralized controller incorporates the addition of auxiliary control terms to the conventional droop controller. The auxiliary control terms are based on the total real and reactive power generation information acquired from wide area measurement system through PMUs and the desired power sharing of each IIDG unit. The secondary-level centralized controller, on the other hand, enhances the performance of each local decentralized controller by compensating the voltage and frequency deviations caused by the load disturbances. The performance of the proposed hierarchical controller has been demonstrated through eigenvalue analysis and time-domain simulation results carried out in MATLAB/SIMULINK environment. Further, in order to have a fair comparison, the performance of the proposed hierarchical controller, based on modal-based extended linear quadratic Gaussian (LQG) approach, has been compared with that of hierarchical controller based on state-based extended LQG approach. Simulation results revealed the capability of the proposed hierarchical controller to mitigate the unstable oscillations as well as to settle quickly at different operating points under the application of small-signal disturbances.

Enhanced Two-Stage Hierarchical Control for a Dual Mode WECS-Based Microgrid

Along with the great benefits of utilizing renewable energy (e.g., wind energy) in the power system, there are also some issues, such as increasing the uncertainty and reducing the system inertia. Communication-based centralized control has started to play a significant role in reacting to the aforementioned issues, especially for relatively small systems, such as microgrids. In this context, in this paper, an enhanced communication-based hierarchical control for a dual mode wind energy conversion system-based microgrid is modeled and investigated. The primary stage utilized the P-V/Q-f droop method, which is the preferred droop method to be used in microgrids when the line impedance is mainly resistive. The secondary stage relied on an enhanced methodology for compensating the deviations of voltage and frequency and improving the performance of the microgrid during small and large signal disturbances. Moreover, as this microgrid operates in a dual mode, the mode transition cases from grid-tied mode to autonomous mode and vice versa have been addressed. Thereafter, an improved control scheme for the unplanned outage transition and a modified control scheme for the pre-synchronization and reconnection transition were proposed. Finally, the proposed work was evaluated by the simulation results in MATLAB environment.

Power System Stability Analysis of SMIB with FOPID using Cuckoo Search Optimized Differential Evaluation

Due to complexity in the power system there is always a loss of the stability due to the fault. Whenever a fault is intercepted in system, the whole system goes to severe transients. These transients cause oscillation in phase angle which leads poor power quality. The nature of oscillation is increasing instead being sustained, which leads system failure in form of generator damage. To reduce and eliminate the unstable oscillations one needs to use a stabilizer which can generate a perfect compensatory signal in order to minimize the harmonics generated due to instability.This paper presents a Power System stabilizer to reduce oscillations due to small signal disturbance. Additionally, a hybrid approach is proposed using FOPID stabilizer with the PSS connected SMIB. Cuckoo Search (CS) Optimized Differential Evaluation (DE) approach is used for the parameter tuning of the stabilizer. The efficiency of proposed approach is observed by rotor angle and power angle deviations in the SMIB system.

Coordinated Control Strategy of Distributed Energy Resources based Hybrid System for Rural Electrification

This paper proposes coordinated active and reactive power control strategy of wind-biogas based hybrid system for rural electrification (HSRE) in order to provide continuous and reliable source of electricity to a cluster of villages. In the control strategy used for HSRE, a predefined part of load is being supplied by the grid and the remaining part, under steady state as well as small signal disturbances, is taken care by a hybrid system of controllable and intermittent sources of energy. Induction generator (IG) based wind energy conversion system (WECS) has been considered as a source for HSRE. Since reactive power is needed by both IG and load, an additional source of reactive power, static synchronous compensator (STATCOM) is used to fulfill the reactive power requirement. The synchronous generator has been used for power generation from biogas-genset which is fitted with electronic speed governor and automatic voltage regulator (AVR). The concept of defined grid operation is achieved by considering dynamics of system voltage angle as well which cannot be achieved by the usual control techniques for frequency and voltage magnitude. The developed hybrid system is given a small signal disturbance in load as well as input wind power. The robustness of proposed control strategy has been showed from the dynamic performance results by maintaining power balance between system components while regulating the system voltage and frequency.

Model order reduction analysis of DFIG integration on the power system small‐signal stability considering the virtual inertia control

In view of the problem that the detailed model of doubly-fed induction generator (DFIG) considering virtual inertia control is high ordered and difficult to analyse, a reduced-order model for DFIG that is applicable to small-signal stability analysis is presented. First, according to the attenuating speed of each state variable, the dynamic characteristics of different components of DFIG are explored from the time scale perspective. On this basis, considering the electromechanical coupling characteristic of DFIG, the third-order simplified model retaining the dynamic of virtual inertia control and phase-locked loop is derived. Moreover then, the dynamic model of inter-connected system with reduced-order model integration is established. Finally, the attenuation time constant of each state variable of DFIG detailed model is calculated. Simulation tests on the New England 10-generator 39-bus test system verify that compared with detailed model of DFIG, the presented reduced-order model could reflect the dynamic characteristics of power system under small-signal disturbance more accurately, with greatly reduced computation amount.

Advanced control strategy on battery storage system for energy management and bidirectional power control in electrical networks

This paper introduces an advanced control strategy on battery energy storage systems (BESS) for bidirectional power control and stability improvement. The proposed control strategy efficiently controls the charging-discharging states of BESS as well as provides bidirectional control on both active and reactive powers. The introduced control scheme is equipped with supplementary stabilizers to damp out the oscillations and stability improvement. The problem of designing the controllers is mathematically expressed as a constrained optimization programming and solved by particle swarm optimization (PSO). The results show that the proposed control strategy can efficiently control both active and reactive powers independent of each other. As well, it is able to change the direction of both active and reactive powers from positive to negative and vice-versa. The designed stabilizers also improve stability of the network and damp out the oscillations following large-signal and small-signal disturbances.