Subsynchronous Oscillation Problem Research Articles

Subsynchronous oscillation analysis method based on broad learning system

This paper presents a method to analyze the Sub Synchronous Oscillation (SSO) problem based on broad learning system (BLS), which can quickly analyze the risk of SSO in a system and take measures. The simulation system is constructed by the eigenvalue analysis method to obtain training data, that solves the problem which is difficult to obtain actual data in SSO problem and makes the model more accurate and the conclusion more convincing. Subsequently, BLS is applied for feature extraction and the prediction model is constructed, the model can show the deep relationship between the oscillation source and topology of the system as well as various operating data, which is difficult to be expressed by formula. The system was tested and validated in the 41-bus system. The feature importance analysis method which comes from eXtreme Gradient Boosting (XGboost) algorithm is proposed and combined with the BLS prediction model, which can analyze the influence of each variable on the prediction results in different series compensation levels, and is validated in the 41-bus system, that makes the results of prediction more interpretable. Finally, the results of simulation show that the model can predict data with high accuracy and give adjustment plans for effective control of the system to avoid the risk of SSO.

Sub-synchronous oscillation suppression in MMC-HVDC grid-connected systems under wind farm fluctuation scenarios

In order to solve the problem of sub-synchronous oscillation (SSO) of wind power grid-connected system with modular multilevel converter based on high voltage direct current transmission (MMC-HVDC), which is characterized by frequency drift due to the fluctuation of wind power output and the dynamic interaction of MMC. By considering the coupling characteristics of wind power volatility and the internal harmonic dynamics of MMC, we establish a small-signal model of the interconnection system between the equivalent wind farm and MMC-HVDC, study the dominant factors triggering the system oscillation, and use model predictive control (MPC). The results show that the wind farm output, wind farm terminal voltage and terminal current are the dominant factors leading to SSO frequency drift. It is also verified that the MPC-SSDC control not only effectively suppresses SSOs with single frequency drift, but is also effective when multiple SSOs with different frequencies exist simultaneously. It is shown that MPC-SSDC can self-adapt to the multi-oscillation scenario of wind power grid-connected system to provide frequency and damping support for the system.

Design of polar coordinate vector current control strategy for VSC connected to weak power grid

In order to solve the problem of subsynchronous oscillation when voltage source converter is connected to weak power grid, according to the design steps of the modern control theory based on the state space method, this paper designed a control strategy of the converter, which can effectively improve the stability of the weak synchronous system. Modern control theory takes into account all independent state variables from input to output, thus it can connect the internal state of the system with the external input and output effectively.The paper constructed the state equation of weakly synchronous AC system in static coordinate system, and then the polar coordinate representation of the system state equation is obtained by using complex transformation and Euler equation. The vector current control object of VSC is the vector current injected into the weak AC power grid. By adjusting the injection current of the weak AC power network in the amplitude direction and phase direction of the polar coordinates, the stability control of the VSC connected to the weak AC power grid is realized. Finally, the effectiveness and stability of the designed control strategy are verified by electromagnetic transient numerical simulation.

Online Monitoring and Early Warning of Subsynchronous Oscillation Using Levenberg–Marquardt and Backpropagation Algorithm Combined with Sensitivity Analysis and Principal Component Analysis

Over the past few years, with the access of large-scale new energy sources, the problem of subsynchronous oscillation (SSO) in power systems has presented a novel multisource and multitransformation form, which may be significantly threatening. Conventional control and protection methods primarily give rise to device protection actions in the presence of severe oscillation. On the whole, online monitoring only identifies the frequency and amplitude, whereas it cannot identify the attenuation factor. Moreover, the determination of the warning threshold is more dependent on human experience, so the reliability and rapidity of the early warning cannot be ensured. This study conducts an in-depth investigation of the wind-thermal power bundling and extreme high-voltage alternating current- (AC-) direct current (DC) hybrid transmission system. The major factors of SSO using this system are unclear, which brings difficulties to effective monitoring. Given the mentioned problems, a method combining Levenberg–Marquardt- (LM-) Backpropagation (BP) machine learning and Sensitivity Analysis (SA) and principal component analysis (PCA) is developed. First, the sensitivity analysis of each factor in the system is conducted to identify the major factors of SSO. Subsequently, the historical sample data are reduced with the principal component analysis to reduce the redundancy, which is adopted to train the regression model to determine the attenuation factor and frequency and then send them to the classifier for classification to complete the task of the assessment model. When a novel data signal is uploaded, the assessment model identifies the attenuation factor and frequency and subsequently determines the presence of SSO. Accordingly, an early warning is conducted. The system's refined simulation model and machine learning model verify the effectiveness of the method.

Analysis of Subsynchronous Torsional of Wind–Thermal Bundled System Transmitted via HVDC Based on Signal Injection Method

With the development of large-scale new energy, the wind–thermal bundled system transmitted via high-voltage direct current (HVDC) has become the main method to solve the problem of wind power consumption. At the same time, the problem of subsynchronous oscillation among wind power generators, high-voltage direct current (HVDC), and synchronous generators (SGs) has become increasingly prominent. According to the dynamic interaction among doubly fed induction generators (DFIGs), HVDC, and SGs, a linearization model of DFIGs and SGs transmitted via HVDC is established, and the influence of the electromagnetic transient of wind turbines and HVDC on the electromechanical transient processes of SGs is studied. Using the method of additional excitation signal injection, the influence of the main factors of DFIG on the damping characteristics of each torsional mode of SG is analyzed, including control parameters and operation conditions when the capacity of HVDC is fixed. The mechanism of the negative damping torsional of SGs is identified. A time-domain simulation model is built in Electromagnetic Transients including DC/Power Systems Computer Aided Design (EMTDC/PSCAD) to verify the correctness and effectiveness of the theoretical analysis.

Modal parameter identification of subsynchronous oscillation based on stochastic subspace algorithm

At present, under the general trend of interconnection of power grid systems, the problem of sub-synchronous oscillation of power systems has gradually become the focus of attention. Stochastic subspace modal identification (SSI) algorithm plays an important role in vibration detection and damage identification of large motors. Finally, experiments are performed on the data collected in the field, and the results show that the SSI algorithm can better identify the mode of the signal. Compared with the traditional Prony algorithm and ARMA algorithm, the recognition accuracy of the stochastic subspace algorithm constructed in this paper is higher than that of Prony algorithm and ARMA algorithm, which has the advantage of strong anti-noise.

SSO analysis and SSDC parameter optimisation based on the wind farm connected to HVDC transmission system

The interaction between renewable energy generation and high-voltage direct current (HVDC) transmission system becomes an essential cause of the subsynchronous oscillation (SSO) problem. In this study, the permanent magnet synchronous generator-based wind farm connected to HVDC transmission system is studied. The susceptivity analysis is carried out to find the main influence factors of the SSO problem. Besides, a parameter design method for subsynchronous damping controller is proposed. The configuration and the performance indicator are discussed, and then the optimisation algorithm is developed based on hybrid genetic algorithm and electromagnetic transient simulation. Finally, the proposed design method is validated by simulation in PSCAD/EMTDC.

Study on subsynchronous oscillation in D‐PMSGs‐based wind farm integrated to power system

In recent years, the subsynchronous oscillation (SSO), which occurs in direct-drive permanent magnetic synchronous generators (D-PMSGs)-based wind farm, has great impact on the stability of power system. The different parameters and operation conditions of D-PMSGs lead to the subsynchronous interaction (SSI) among D-PMSGs. What is more, the SSI will influence the SSO characteristics of the system of D-PMSGs-based wind farm integrated to AC network. Here, considering the difference of parameters or operation conditions among D-PMSGs in the wind farm, eigenvalue analysis, based on the small-signal state-space model of two aggregated D-PMSGs which are equivalent to wind farm, is carried out. Then the stability and the SSI between D-PMSGs of the equivalent system can be studied, and the dominant D-PMSG can be determined based on the participation factors. Lastly, the detailed electromagnetic transient simulation model of D-PMSGs equivalent system is built in PSCAD/EMTDC. The simulation is conducted to corroborate the eigenvalue analysis. The result shows that an obvious SSI exists between two aggregated D-PMSGs. Furthermore, the different SSO characteristics among D-PMSGs in the wind farm indicate the study of SSO problem based on an aggregated D-PMSGs model may leave out some useful information.

Studies of Sub-Synchronous Oscillations in Large-Scale Wind Farm Integrated System

With the rapid development and construction of large-scale wind farms and grid-connected operation, the series compensation wind power AC transmission is gradually becoming the main way of power usage and improvement of wind power availability and grid stability, but the integration of wind farm will change the SSO (Sub-Synchronous oscillation) damping characteristics of synchronous generator system. Regarding the above SSO problem caused by integration of large-scale wind farms, this paper focusing on doubly fed induction generator (DFIG) based wind farms, aim to summarize the SSO mechanism in large-scale wind power integrated system with series compensation, which can be classified as three types: sub-synchronous control interaction (SSCI), sub-synchronous torsional interaction (SSTI), sub-synchronous resonance (SSR). Then, SSO modelling and analysis methods are categorized and compared by its applicable areas. Furthermore, this paper summarizes the suppression measures of actual SSO projects based on different control objectives. Finally, the research prospect on this field is explored.

Subsynchronous Oscillation Problem Research in the UHVDC System of a Regional Power Grid in China

Along with the grid structure being more and more complex and the rapid development of the HVDC system, studying the subsynchronous oscillation (SSO) problem on HVDC system has more engineering practice significance. The paper studies subsynchronous oscillations problem of generators near the ±800kV UHVDC converter station, and analyzes the subsynchronous oscillation possibilities through PSCAD/EMTDC simulation. At last, though the researched UHVDC thermal plants have none SSO risk but it needs other measures to make the relevant generators return on normal operation.

Simulation and study on mitigation measures of frequent subsynchronous oscillation with low amplitude at multi-power plants

Subsynchronous oscillation (SSO) with low amplitude that exceeds cumulative fatigue threshold of the generator shaft frequently could significantly reduce the shaft’s service life, which is a new SSO problem that emerges in recent years. According to the real recording oscillograph, the basic reason for frequently over-threshold SSO with low amplitude at multi-power plants was analyzed based on Hulunbuir League system. The sensitivities of the electrical damping to the main electrical parameters in the contributing loop of subsynchronous torsional interaction were calculated. Based on the sensitivities, a simulation method was presented, which was used to excite the same oscillation as the actual case by exerting disturbance on the firing angle. The limitation of wide-band and narrow-band supplementary subsynchronous damping controller (SSDC) for mitigating this kind of SSO was analyzed based on the electromagnetic transient simulation model of Hulunbuir League system. The difference of supplementary excitation damping controller (SEDC) and parallel-form FACTS connected to the generator terminal was compared from the aspects of response time and the ability of damping torque supplying. The analysis indicates that their response time is similar but FACTS has stronger ability of damping torque supplying than SEDC. Time-domain simulation method was used to compare the mitigation effects of SEDC, static var compensator (SVC) and static synchronous compensator (STATCOM). Considering the mitigation effect, the floor space limit of the power plant and so on, STATCOM was considered as the best mitigation measure. A control strategy of cascaded STATCOM for engineering application was presented and the capacity for SSO mitigation as well as output characteristics was analyzed. The analysis indicates that STATCOM using the proposed control strategy has better mitigation effect and output characteristics with smaller capacity.

Power System Subsynchronous Oscillations Electromagnetic and Electromechanical Transient Hybrid Real-Time Simulation Based on RTDS

In this paper, power system electromagnetic and electromechanical transient hybrid real-time simulation technology is expounded in details, which has advantages of the electromagnetic transient simulation program and electromechanical ones. The more details needed to analyze the dynamic characteristics of power systems are provided by this hybrid simulation technology, and the scale of power system simulated is not limited in the hybrid simulation program. The hybrid simulation program is applied to analyze the power system subsynchronous oscillation problem occurred in a power plant with 4 turbine generators located in the northwestern China. According to the simulation results, it is clear that the stability of generators is threatened by the subsynchronous oscillations caused by capacitor series compensation in the transmission line connecting the power plant and the load center system. In meantime, the effectiveness of the countermeasure is validated simultaneously by the hybrid simulation results.