Large-scale Wind Power Transmission Research Articles

Composition and Control of a New Type of Hybrid Voltage-Source Converter Based on DRUs and FB-MMC for Large-Scale Offshore Wind Power Integration and Transmission

Composition and Control of a New Type of Hybrid Voltage-Source Converter Based on DRUs and FB-MMC for Large-Scale Offshore Wind Power Integration and Transmission

Large-signal stability analysis for offshore wind power fractional frequency transmission system with modular multilevel matrix converter

Aiming to achieve zero carbon emission, the rapid development of offshore wind power transmission system faces stability challenge. The fractional frequency transmission system (FFTS) with modular multilevel matrix converter (M3C) holds considerable promise among the solutions for large-scale and long-distance offshore wind power transmission. Currently, numerous demonstration projects involving FFTS are being conducted worldwide, necessitating urgent attention to system stability analysis for practical engineering applications. Notably, conventional approaches focusing on small-signal stability are inadequate when confronted with large-signal disturbances. In this study, the Takagi–Sugeno fuzzy model of FFTS is proposed considering the complex control strategy of M3C and the system strong nonlinearity. Subsequently, the Lyapunov function and the large-signal stability domain of attraction (LS-DOA) are constructed expeditiously based on the proposed fuzzy model. When analyzing the system larger-signal stability, the novel stability strength and optimal optimization factor are further introduced to develop a quantitative and efficient methodology for parameter optimization guidance compared with the conventional method. Thus, the FFTS different-frequency interaction features are elucidated from normal and different characteristics parameters mathematically and comprehensively. The effectiveness of proposed methods is verified by the simulation-based study.

Coordination Control of Wind Farm Integrated Cascaded Hybrid HVDC System in Weak Grids

Combing the benefits of line-commutated converter (LCC) and modular multilevel converter (MMC), the hybrid high-voltage direct-current (HVDC) system is a viable option for the long-distance transmission of large-scale wind power. However, as renewable energy becomes more prevalent, the inertia of power networks will decrease, possibly leading to instability problems. In this scenario, the conventional grid following (GFL) control scheme is no longer applicable, and suitable coordination control strategies are required. This paper proposes two coordinated grid forming (GFM) control strategies for the cascaded hybrid system and evaluates the control performance of different control types. Firstly, the conventional control scheme of the cascaded hybrid HVDC system and problems under weak AC power systems integration are introduced. Then, coordinated grid forming control strategies are proposed, and the control performance of the GFL and GFM control schemes are compared. Finally, the cascaded hybrid HVDC system's electromagnetic transient model is constructed in PSCAD/EMTDC to confirm the efficacy of the proposed coordinated control strategies.

Reactive Power Compensation Configuration of Offshore Wind Power Based on Economic Differential Pressure Theory

The conventional reactive power balance analysis method for offshore wind power transmission projects can be used to obtain many feasible solutions for reactive power compensation configuration, which requires a large number of simulation calculations to eliminate unreasonable schemes. The work is tedious and lacks theoretical guidance. In this paper, the main influencing factors, such as the current carrying capacity of offshore wind power and submarine cable, the mode of real-time power generation, and the reactive power output regulation of the wind turbine itself, are considered. The reactive power balance of offshore wind power transmission projects is derived. Combined with the economic differential pressure theory, the sea-side and land-side configuration methods of high reactance and dynamic reactive power compensation are put forward. On the basis of realizing real-time reactive power balance, the recommended reactive power compensation configuration scheme effectively reduces the active power loss of the transmission project, and at the same time, lowers the bus voltage of each node at sea, thus reducing the high risk of the excessive voltage of offshore wind farm. This project is supported by the Science and Technology Project of State Grid Corporation of China under “Research on multiple temporal and spatial coordinated optimal control theory for medium and long-distance large-scale offshore wind power transmission system” (No. 5100-202155305A-0-0-00).

Resilient DC Voltage Control for Islanded Wind Farms Integration Using Cascaded Hybrid HVDC System

To integrate large-scale islanded onshore wind power with different sizes, this paper proposes an integration system based on the cascaded hybrid HVDC transmission system, which consists of LCC and several MMCs in series connection at the DC side of the rectifier. A large-scale wind farm is connected with one LCC and one MMC while several small-scale wind farms are connected with MMCs directly. Owing to the hierarchical integration arrangement, the operating flexibility can be improved with reduced capacity and the number of step-up interfacing transformers. A resilient DC voltage control is proposed for the integration system to adaptively redistribute power among the converters during wind power fluctuations. Firstly, the topology and operating characteristics of the wind power integration system are introduced. Then, a resilient DC voltage control is proposed to ensure stable operation during wind power curtailments. Finally, a simulation model of the hybrid cascaded HVDC transmission system is built in PSCAD/EMTDC to verify the effectiveness. The research results show that the system provides a new option for long-distance transmission of large-scale islanded wind power.

Estimating the environmental impacts of HVDC and UHVDC lines for large-scale wind power transmission considering height-dependent wind and atmospheric stability

Due to the imbalance of China’s resources allocation, inter-provincial high voltage direct current (HVDC) transmission grid is considered to be the promising solution to solve to the large-scale wind power transmission, which could tackle the reverse regional distribution problem of energy resource and electricity load. In this contribution, a power law profile model of wind speed on embedded atmospheric stability is developed for calculating the height-dependent wind speed. The Monin-Obukhov length is introduced to determine the atmospheric stability. The ion flow environment model considering height-dependent wind speed is proposed to estimate the influence of height-dependent wind on ground-level electric field environment of DC transmission line and the iterative flux tracing method-finite difference is proposed to solve the model. It is observed that the stable, neutral and unstable atmospheric conditions have a large influence on transverse wind speed and then indirectly influence the electric field and ion current environment of DC lines. For the electromagnetic environment of the practical DC line used for the wind power transmission, the proposed model provides a reasonable agreement with measurements from a perspective of practical engineering application.

Steady-state voltage-control method considering large-scale wind-power transmission using half-wavelength transmission lines

Half-wavelength transmission can transmit large-scale renewable energy over very long distances. This paper proposes an improved steady-state voltage-control method for half-wavelength transmission systems considering large- scale wind-power transmission. First, the unique voltage characteristics of half-wavelength lines are deduced based on the distributed parameter model. In the secondary voltage-control level, reactive power-transmission limits of half-wavelength lines are introduced as another control objective except for tracing the pilot bus voltage reference. Considering the uncertainty and fluctuation of wind power, the overvoltage risk-assessment method of half-wavelength lines is presented to determine specific voltage-control strategies. Simulation results demonstrate that the proposed voltage-control method delivers superior tracking performance according to a voltage reference value and prevents the overvoltage risk of half- wavelength lines effectively in different wind-power penetrations.

Analysis of SSO in DFIG grid with series compensation

Doubly fed induction generator (DFIG) has become the most widely used type of wind power generation due to its superior technical performance. Series compensation technology is widely used in large-scale and long-distance wind power transmission system because of its high cost performance and significant improvement of transmission capacity. However, it may cause subsynchronous oscillation (SSO). This paper first introduces the definition and harm of subsynchronous oscillation, and then analyzes the advantages and disadvantages of series compensation technology, as well as the mechanism and suppression measures of subsynchronous oscillation of DFIG connected system through series compensation. Through modeling and simulation analysis, the suppression effect of additional subsynchronous damping controller (SSDC) on subsynchronous oscillation of DFIG control system is verified.

A Storage and Transmission Joint Planning Method for Centralized Wind Power Transmission

Centralized delivery has become the main operation mode under the scaled development of wind power. Transmission channels are usually the guarantee of out-delivered wind power for large-scale wind base. The configuration of transmission capacity, which has the features of low utilization and poor economy, is hardly matching correctly due to the volatility and low energy density of wind. The usage of energy storage can mitigate wind power fluctuations and reduce the requirement of out-delivery transmission capacity, but facing the issue of energy storage cost recovery. Therefore, it is necessary to optimize the allocation of energy storage while considering the problem of wind power transmission. This paper studies the joint optimization of large-scale wind power transmission capacity and energy storage, reveals the mechanism of energy storage in order to reduce the power fluctuation of wind power base and slow down the demand of transmission. Then, analyze the multi-functional cost-sharing mode of energy storage, improve the efficiency of energy storage cost recovery. Constructs the coordination optimization configuration model to deal with the problem of large-scale wind power transmission capacity and energy storage, and realizes the transmission capacity optimization coordination and optimization with energy storage. The proposed method is verified by a wind base located in Northeast China.

Fast optimal power allocation algorithm for multi‐terminal AC/DC hybrid grids with wind power integration

Multi-terminal alternating current (AC)/direct current (DC) hybrid transmission technology is a promising alternative for the integration and transmission of large-scale wind power. Optimal power allocation (OPA), to distribute the active power between AC and DC transmission lines in order to minimise transmission power loss, is a significant problem to be solved. A new simplified OPA algorithm for multi-terminal AC/DC hybrid grids is proposed in this work. The power flow models of the AC grid and DC grid are separately established and linearised, and both AC and DC power losses are formulated in a simplified way. By doing so, the mathematical formula of the total power loss is expressed as a multivariate quadratic function, of which the minimum value can be directly obtained with the derivative method. Simulations based on a four-terminal AC/DC hybrid grid with wind power integration are carried out by using MATLAB, and the effectiveness of the proposed algorithm is validated by case studies.

Studies of Sub-synchronous Oscillation Caused by the Series Compensation Transmission in System with Large-Scale Wind Power

In recent years, the technology of wind power developed very rapidly, In order to solve the issue of wind power consumption and improve the utilization of wind power. Large-scale wind power transmission is imperative. Series compensation technology is currently one of the economic and effective measures to solve large-scale wind power transmission. However, after the series compensation, sending wind power will cause sub-synchronous oscillation. In this paper, firstly, the structure and characteristics of three common wind turbines are introduced, and then they are summarized according to the characteristics of various turbines. The generation mechanism, related characteristics, and suppression measures of subsynchronous oscillations caused by series complement sending. The analysis method of the subsynchronous oscillation of the current large-scale wind power sending system is described. Finally, the part that needs further research is explained.

Variation characteristics of regional synchronous wind in Hami, Xinjiang of Northwest China

From several towers in Hami, Xinjiang of Northwest China, built by the national wind power resources professional observation network, we selected three towers with synchronous 10-min average wind speed data for one year (May 2011–April 2012) under strict quality control. The towers are located where large-scale wind power development is projected. We analyzed the frequency and variation of extreme wind speed at low wind condition (LWC), rated wind condition (RWC), and cut-out wind condition (CWC), which may significantly impact the electric power grid configuration in large-scale wind power development. The correlation between duration and frequency of LWC/RWC/CWC is obtained. Major findings are: 1) The frequency of CWC is the lowest among all conditions, its synchronous rate at all three towers tends to be zero, and the frequency of LWC is always greater than that of RWC. 2) Among the three towers, the synchronous rate of RWC steadily increases with height, and LWC differs little between different levels. The synchronous rate of LWC concentrates in winter, while that of RWC mainly occurs in spring and summer. Diurnal variation of LWC/RWC during the entire year is significantly different. 3) During the study year, the longest durations of synchronous LWC and RWC among the three towers are up to 640 and 700 min, respectively. The duration and frequency of LWC/RWC can be quantitatively well described by a logarithmic function. Consequently, the synchronous rates of LWC and RWC over any duration in the region can be easily calculated by using the fitting function equation from observed data. These results are of value to the planning of large-scale wind power transmission and grid dispatching in this area.

An Isolated Industrial Power System Driven by Wind-Coal Power for Aluminum Productions: A Case Study of Frequency Control

Due to the uneven geographical distribution between load and wind power, currently it is difficult to integrate the large-scale wind power into the State Grid in China. There are significant wind curtailments for wind farms due to system restrictions. This paper proposes a new way of utilizing wind power, i.e., in-situ consumption, as an alternative to the costly development of long-distance transmission of large-scale wind power. Electrolytic aluminum load, which is one of the most typical high energy consuming loads, is employed to absorb the excess wind power in western China. An actual isolated industrial power system for aluminum production driven by wind power and coal-fired power is described. The penetration level of wind power in the isolated power system is up to 48.8%. The power imbalance between generation and load demand caused by wind power fluctuation or the tripping of coal-fired generators can dramatically impact the frequency stability of the isolated power system, which is of small inertia. An online identification method of power imbalance based on Wide Area Measurement System (WAMS) is presented. According to the characteristics of the electrolytic aluminum load, a system frequency control method by regulating the bus voltages of aluminum loads to eliminate the power imbalance is introduced. The simulation is done in Real Time Digital Simulator (RTDS) and the results verify the validity of the proposed frequency control method.

Impact of Large Scale Wind Power Transmission on System Dynamic Stability

With the scale of the wind farm growing fast, its impact on the power system has become increasingly apparent. So the research has a significant meaning on the characteristics of dynamic stability of the power system which contains wind farms, and the stable operation of the large area interconnected power grid. In this paper it realized the application of the double-fed wind turbine grid model by using power system analysis software PSD-BPA. The analysis of the generator power Angle curve which indicate the state after the failure of N-1 shows as follows: with the wind farms integration on the grid, the damping ratio is decreased slightly but little change after the system failure of N-1, which is still live up to the standard of grid stability.

Overview of Sub-synchronous Oscillation in Wind Power System

Nowadays with the improvement in the degree of emphasis on new energy, the wind power system has developed more and more rapidly over the world. Usually the wind plants are located in the remote areas which are far from the load centers. Generally series compensated AC transmission and high voltage DC transmission are made use of to improve the transmission capacity as two main effective ways which can solve the problem of large scale wind power transmission. The paper describes the three kinds of impact varieties and impact mechanisms in the sub-synchronous oscillation phenomena of wind power system based on doubly fed induction generator (DFIG) wind generators. At last, we point out the important problem that should be stressed in the wind power system.

Collaborative Transmission Planning: California's Renewable Energy Transmission Initiative

Transmission planning has been conducted primarily by utilities, in reactive fashion. Project approvals are increasingly litigated, when stakeholders later become engaged. Large Renewable Energy Standard (RES) targets present additional challenges for approval of generation and transmission projects and often require a proactive development approach. In response, California agencies formed a stakeholder-led planning process, the Renewable Energy Transmission Initiative (RETI) in 2007. RETI identified and ranked Renewable Energy Zones in California and neighboring regions, using both economic and environmental criteria, determined the transmission needed, based on least-regrets transmission planning principles, to access and deliver target renewable energy, and prepared a statewide conceptual transmission plan. RETI has been effective in identifying development priorities and in building stakeholder support for generation-transmission development for renewable energy. Its approach is applicable to other jurisdictions considering large-scale wind power-transmission construction.