Large Disturbance Conditions Research Articles

The ping-pang variable amplitude limiter used in the coordinated controller of a hybrid reactive power compensation system

The hybrid reactive power compensation system, which connects different reactive power compensation devices to the same bus, will be essential equipment for future power systems. In a power grid with a high proportion of photovoltaic, wind turbines, and power electronic devices, it is significant to design a coordinated control strategy for the hybrid reactive power compensation system. In this paper, a kind of ping-pang variable amplitude limiter is used in the linear optimal controller. The ping-pang variable amplitude limiter can improve the transient stability of a hybrid reactive power compensation system. The effects of the coordinated controller are verified in simulation. Compared with the conventional linear optimal controller, the coordinated controller with the ping-pang variable amplitude limiter has a better optimization effect in large disturbance conditions.

Coordinated Design of Type-2 Fuzzy Lead–Lag-Structured SSSCs and PSSs for Power System Stability Improvement

This work suggests a type-2 fuzzy lead–lag (T2FLL) controller structure for flexible AC transmission system (FACTS)-based damping controllers and power system stabilizers (PSSs) for power system stability improvement. The values of the suggested controller are optimized by a hybrid adaptive differential evolution and pattern search algorithm (hADE-PS) method. Initially, a single-machine infinite-bus (SMIB) system with lead–lag (LL)-structured FACTS and PSS controllers is considered, and the dominance of the hADE-PS method is established over the original differential evolution (DE), genetic algorithm (GA), and particle swarm optimization (PSO). The supremacy of T2FLL over the lead–lag (LL) controller is established under different large and small disturbance conditions, as well as varied loading conditions and fault positions. Lastly, the effectiveness of T2FLL is evaluated in a multimachine power system (MMPS). It is demonstrated that the suggested T2FLL offers better performance than the LL controller under various large and small disturbance conditions by providing significantly more damping to all modes of oscillations.

Dynamic modeling for VSG cluster by using data-physical driven method

In the task of system analysis for VSG cluster, aggregation modeling method is widely used for simplification. However, there are inevitable errors occur from the process of cluster aggregation. To improve the accuracy of VSG cluster modeling, a data-physical driven modeling method is presented. At first, the equivalence between aggregation error and black box modeling issue is analyzed. Secondly, a hybrid model structure is proposed, which consists of single machine aggregation model and deep neural network based aggregated-error model. Then, to illustrate the modeling procedure, test cases are studied under large disturbance and multi-operating points conditions. The simulation results confirm that the proposed method can provide satisfactory modeling accuracy.

MPC-Based Coordinated Voltage Regulation for Distribution Networks With Distributed Generation and Energy Storage System

This paper presents a model predictive control (MPC)-based coordinated voltage control scheme for distribution networks with high penetration of distributed generation (DG) and energy storage. In this scheme, the DG units, energy storage devices, and on-load tap changer are optimally coordinated to maintain all bus voltages in the network within a permissible range. To better coordinate the economical operation and voltage regulation, two control modes are designed according to the operating conditions. In the preventive mode, the DG units operate in the maximum power point tracking mode. State-of-charge of energy storage system (ESS) units and power outputs of DG and ESS units are optimized while maintaining the voltages within the feasible range. In the corrective mode, active power curtailment of DG units is also used as a necessary method to correct the severe voltage deviations. The voltage sensitivity coefficients with respect to the power injections and tap changes are updated in real time using an analytical sensitivity calculation method to improve the computation efficiency. A test system consisting of two 20-kV feeders fed from the same substation based on a real distribution network was used to validate the proposed coordinated voltage control scheme under both normal and large-disturbance conditions.

Distributed voltage regulation of smart distribution networks: Consensus-based information synchronization and distributed model predictive control scheme

This paper proposes a distributed voltage control (DVC) scheme for smart distribution networks with high penetration of inverter-based distributed generators (DGs), aiming to optimally coordinate DG units and on load tap changer (OLTC) transformer to regulate the voltages within the feasible range. The proposed scheme consists of two important parts: (1) distributed information synchronization (DIS) framework and (2) distributed model predictive control (DMPC)-based voltage control scheme. The DIS framework is established based on the consensus protocols to synchronize the specific information about the critical bus voltages and potential OLTC actions. The DMPC-based voltage control scheme is presented, in which each DG unit only exchanges information with its immediate neighbors and solves the local optimal control problem. Two control modes are designed to better deal with different operating conditions. In the normal mode, only the reactive power outputs of DG units are optimized to mitigate the voltage deviations. In the corrective mode, both of the active and reactive power outputs of DG units are optimally controlled to correct the severe voltage deviations. To mitigate the mutual interaction between the DGs and OLTC, the potential actions of OLTC are predicted and considered in the optimization problem of each units. The control performance of the proposed scheme was demonstrated using a real medium-voltage (MV) distribution network with two feeders under both normal and large-disturbance conditions.

Model Reduction of DFIG Wind Turbine System Based on Inner Coupling Analysis

The doubly-fed induction generator (DFIG) wind turbine system, which is composed of the wind turbine, generator, rotor-side converter, grid-side converter, and so on, is a typical multi-time scale system. The dynamic processes at different time scales do not exist in isolation. Furthermore, neglecting the coupling of parameters of different time scales to reduce the order of the model will lead to deviation between the simulation results and the actual results, which may not be suitable for power system transient analysis. This paper proposes an electromechanical transient model and an electromagnetic transient model of the DFIG wind turbine system that consider the interaction of multiple time-scale dynamic processes. Firstly, the paper applies the modal analysis method to explain the multi-time scale characteristics of the DFIG wind turbine system. Secondly, the variation in the eigenvalues of the DFIG wind turbine system before and after the order reduction and the coupling between variables and the system, as well as the coupling between variables of different time scales, are analyzed to obtain the preliminary 21-order simplified model. Thirdly, considering the weak coupling characteristics between the mechanical part and the electromagnetic part of the DFIG wind turbine system, the 21-order simplified model is decomposed into a 15-order electromagnetic transient model and a six-order electromechanical transient model on the basis of their time scales. Then, according to the balance between simulation time and simulation accuracy, the 14-order electromagnetic transient model and the 10 or 12-order electromechanical transient model are finally obtained. Finally, the rationality of the simplified models is verified by simulations under two large disturbance conditions, namely wind speed abrupt change and voltage sag. The obtained simplified models have reference significance for improving the simulation speed of a wind power grid-connected system and analyzing the internal mechanism of the DFIG wind turbine system’s stability.

Restraining SSR with CDRPF-signal supported static var system

Abstract A new supportive signal namely Combined Derivative of Reactive Power and Bus Frequency (CDRPF) in SVS for alleviating torsional oscillations due to SSR is developed. The IEEE first benchmark model incorporating midpoint located SVS is considered as a test system. The effect of CDRPF-SVS supportive signal for restraining torsional oscillations due to SSR is illustrated. An analysis through eigenvalues of the linearized series compensated power system is demonstrated once incorporating the proposed supportive signal and once without any supportive signal. It is found that the unstable torsional modes are effectively eliminated with the proposed supportive signal. Also, the performance of the proposed supportive signal is assessed for the non-linear system model under large disturbance conditions. The concept of designing of proposed supportive signal has been implemented by using a detailed system model reflecting the system dynamics of various power system components accurately. Results of simulation demonstrate the effective damping of torsional oscillation due to subsynchronous resonance (SSR) under severe conditions and confirm the efficacy of the supportive input signal under consideration.

Piecewise Average-Value Model of PWM Converters With Applications to Large-Signal Transient Simulations

State-space average-value models (AVMs) of pulse width modulation converters are widely used in both small-signal frequency-domain analysis and large-signal time-domain transient simulations. This paper is focused on the latter category. The limitations of the traditional state-space AVM (T-AVM) are discussed. A piecewise state-space AVM, P-AVM, is proposed, which uses the actual duty ratio as the control input instead of the continuous duty ratio used by the T-AVM. In order to consider the effect of switching ripples, an approximate ripple function is obtained. An iterative algorithm is proposed for utilization of P-AVM and ripple function for large-signal time-domain transient simulations. A boost converter and a two-level three-phase ac–dc converter are used to validate the performance of the P-AVM in comparison with the T-AVM under large ripple and large disturbance conditions. The detailed models developed in PSCAD/EMTDC are used as benchmarks. Improvement in accuracy is demonstrated. The efficiency of the iterative algorithm is discussed. Experiments on a 50-kVA three-phase ac–dc converter are conducted to validate the proposed method.

Adaptive Control Using Constrained RLS and Dynamic Pole-Shift Technique for TCSCs

In this paper, an adaptive pole-shift control technique for a FACTS device, namely Thyristor Controlled Series Capacitor (TCSC), is presented. Adaptive pole-shift techniques have been successfully implemented for power system stabilizer applications in the past, but one of the difficulties in extending such a technique for transmission line control devices has been its inability to handle large disturbance conditions such as three-phase faults. In recent literature, random walk technique has been suggested during the system identification process, to overcome this problem. This paper presents a simple parameter constrained RLS identification procedure to track the large disturbance conditions. The effectiveness of the proposed methodology is demonstrated using (i) a three-area six-machine power system with a TCSC, and (ii) a IEEE 12 bus power system configuration with a TCSC.

Coordinated Control of SVS and CSC for Damping Power System Oscillations

In this paper the effectiveness of Static Var System (SVS) auxiliary controller in coordination with controlled series compensation has been demonstrated for damping power oscillations for wide range of operating conditions. A new SVS auxiliary controller, known as the combined derivative of reactive power and derivative of computed internal voltage (CDRPDCIV) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of a series compensated long transmission line to get most effective damping effect. The first IEEE benchmark model for analysis of torsional modes has been adopted. Eigen value analysis study is conducted for various levels of power transfer and series compensation. The results of eigen value analysis are validated by carrying out time domain analysis study based on non linear model. The proposed SVS auxiliary controller in coordination with CSC with its bang - bang form of control is very effective in damping power system oscillations over a wide operating range under large disturbance conditions thus enhancing the Transient performance of the power system.

Damping subsynchronous resonance in power systems

An idea is presented for damping SSR in power systems using a double-order SVS auxiliary controller in combination with continuous controlled series compensation (CCSC) and an induction machine damping unit (IMDU) coupled with the T–G shaft. A linearised dynamic model of continuous controlled series compensation has been derived and incorporated. The eigenvalue analysis using the linearised model for continuous operation of CSC in combination with an induction machine damping unit (IMDU) and a double-order SVS auxiliary controller (DOAC) has been applied. It is seen that all the unstable torsional modes of various frequencies are stabilised effectively. A time-domain modulation study has also been performed using the nonlinear model to demonstrate the effectiveness of the proposed scheme under large disturbance conditions. The scheme enhances the system performance considerably and torsional oscillations are damped out at all levels of series compensation and effective control of power flow is obtained.

Sliding mode control with perturbation estimation: application to motion control of parallel manipulator

Sliding mode control (SMC) incorporated with perturbation compensation is developed here to reduce the low-frequency tracking error in the presence of wide-band frequency perturbations for a nonlinear dynamic system. The control scheme is then applied to the motion control of a two-degree-of-freedom (DOF) parallel manipulator, utilizing its reduced dynamics for real-time implementation. It is shown that the SMC with perturbation compensation is far superior to the conventional SMC in tracking control of the manipulator under large payload and external disturbance conditions.

Identification of exciter constants using a coherence function based weighted least squares approach

Experience with generator exciter modeling at the Ta-Kuan pumped storage power plant in Taiwan is reported. To identify exciter parameters, frequency response data are first obtained by injecting wide bandwidth signals into the system. Then a modified weighted least squares (WLS) approach using a coherence function is developed to determine exciter constants. A novel feature of the proposed coherence function based WLS method is that it can eliminate measurement dependent inaccuracies by placing less weights on measurements that are more severely corrupted by noise. Based on the established excitation system model, computer simulations are performed to examine the dynamic responses of the generating unit under small and large disturbance conditions. Field test results are also provided. >

Performance testing of a long distance radial static VAr compensated transmission system and validation of simulation results

The authors present selected results of recent field tests carried out on the 220 kV, 660 km radial static VAr (volt-ampere reactive) compensated Muja-Kalgoorlie transmission system in Western Australia. Measured results on network harmonics, SVC (static VAr compensator) losses and the responses of the power system under small and large-disturbance conditions are discussed. The recorded data have also been used to validate and improve the computer models used in simulation studies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>