New Concept for Calculating DC Harmonic Voltages and Currents in BTB HVDC Converters

This paper deals with a new concept for calculating DC harmonic voltages and currents of line- commutated HVDC systems. In contrast to the conventional method, this method is useful for BTB (Back-To-Back) HVDC systems without smoothing reactors or PTP (Point-To-Point) with very short transmission line. This method proposes a new direction for HVDC system design and analysis. The proposed method is applied to a 50 Hz/60 Hz BTB test system and a synchronized BTB test system. After simulation and verification, the new results are introduced.

Comprehensive predictive control of neutral-point voltage balancing for back-to-back three-level NPC converters

A comprehensive predictive strategy was proposed for the neutral-point balancing control of back-to-back three-level converters. The phase currents at both sides and the DC-link capacitor voltages were measured for the prediction of the neutral-point current. A quality function was found to balance the neutral-point, and a metabolic on-times distribution factor was used as a predicator to minimize the quality function at each switching state. Simulation results show that the proposed method produces smaller ripples in tested signals compared with the established one, namely, 9.15% less in a total harmonic distortion(THD) of line-to-line voltage, 1.08% less in the THD of phase current, and 0.9 V less in the ripple of the neutral-point voltage. The obtained experimental results show that the main harmonics of the line-to-line voltage and the phase current in the proposed method are improved by 10 d B and 6 d B, respectively, and the ripple of neutral-point voltage is halved compared to the established one.

The first localized back-to-back converter station started expansion

The first fully localized back-to-back DC intercon-nection project which connects Northwest and CentralChina power grids, 330-kV Lingbao Converter Stationhas now started construction for expansion.Lingbao back-to-back converter station situated inLingbao City of Henan Province is the first DC intercon-

Enhanced control of DFIG-used back-to-back PWM VSC under unbalanced grid voltage conditions

This paper presents a unified positive-and negative-sequence dual-dq dynamic model of wind-turbine driven doubly-fed induction generator(DFIG) under unbalanced grid voltage conditions. Strategies for enhanced control and operation of a DFIG-used back-to-back(BTB) PWM voltage source converter(VSC) are proposed. The modified control design for the grid-side converter in the stationary αβ frames diminishes the amplitude of DC-link voltage ripples of twice the grid frequency,and the two proposed control targets for the rotor-side converter are alternatively achieved,which,as a result,improve the fault-ride through(FRT) capability of the DFIG based wind power generation systems during unbalanced network supply. A complete unbalanced control scheme with both grid-and rotor-side converters included is designed. Finally,simulation was carried out on a 1.5 MW wind-turbine driven DFIG system and the validity of the developed unified model and the feasibility of the proposed control strategies are all confirmed by the simulated results.

Complete Localization of HVDC Back-to-Back Project Realized

The first completely localized DC back-to-back project for asynchronous interconnection between Northwest and Central China plays an important role in realizing national power grid interconnection, spurring indigenous manufacturing industries and promoting DC transmission equipment. Insisting on the principle of autonomous innovation, this project was based on domestic forces in every aspect, from engineering organization, system design, equipment completion, engineering design, equipment manufacturing and procurement to construction and debugging. By passing through strict quality control, intermediate supervision and acceptance test and assessment, the project has been proved up to world advanced level.

Consensus control of electric spring using back-to-back converter for voltage regulation with ultra-high renewable penetration

Recent advances in a power electronic device called an electric spring(ES)provide feasible solutions to meeting critical customers’requirements for voltage quality.A new version of the ES was introduced based on a back-to-back converter(ESBC)configuration which extends the operating range and improves the voltage suppression performance to facilitate ultra-high renewable penetration.This paper proposes an efficient control method to facilitate the voltage regulation function of an ESBC with non-critical loads.Particularly,the proposed method is suitable for various load characteristics.We also develop a consensus algorithm to coordinate multiple ESs for maintaining critical bus voltage in distribution systems with ultra-high renewable penetration.The proposed operation of the ESBC is verified by simulation of a modified IEEE 15-bus distribution network.The results show that the ESBC can effectively regulate system voltage and is superior to the original version of the ES.

灵宝背靠背直流工程系统调试中的关键技术分析

灵宝背靠背直流联网输电工程是我国直流输电国产化的示范工程,该工程的系统调试是第一次依靠国内技术力量调试全部国产化设备。介绍了系统调试中几个关键技术问题的分析和解决过程:系统调试方案的编写过程;在换流站两侧均为单回交流进线的情况下交流系统单相瞬时故障点的选择和试验方法;最后断路器跳闸功能的原理、配置原则及软件和硬件的完善;换流站阀冷却变频器控制保护功能的完善。这几个关键技术问题的解决保证了系统调试的完成以及该工程的顺利投入运行。

中国—俄罗斯背靠背联网工程500kV交流出线具有自动重合闸的直流控制策略

为提高中俄直流联网黑河换流站跨国联网工程运行的可靠性,提出了修改故障期间直流控制策略的方案,以使工程原设计方案中未设置的自动重合闸功能恢复使用。采用EMTDC仿真软件建立模型进行典型工况计算,并对重合闸期间产生的交流母线过电压、交流母线避雷器和阀避雷器的耐受能力进行了校核比较。仿真结果表明,新的控制策略应限制故障期间功率水平在300MW(标幺值为0.4)以内。修改后的控制策略在黑河换流站实施后,通过兴福变至黑河变(兴黑线)故障后重合闸的实践检验,证明了策略的可行性和可靠性。所得出的直流控制策略对研究弱交流系统条件下换流站仅有1回交流出线时采用自动重合闸功能有重要指导意义。

灵宝换流站顺序控制和联锁

基于换流站控制保护系统的引进技术研究了西北—华中直流联网背靠背工程灵宝换流站的顺序控制和联锁,提出的实施方案(包括功能、性能及步骤的规定)通过了成套设计审查,由厂家根据成套设计方案生产设备,并通过了在北京的联合功能及性能测试。

三相四线制背靠背变换器零电压开关技术

提出了一种零电压开关ZVS(zero-voltage-switching)三相四线制背靠背BTB(back-to-back)变换器拓扑及齐边沿脉宽调制EA-PWM(edge aligned pulse width modulation)方法,辅助开关仅需要在每个开关周期内动作一次,就可以实现BTB变换器中所有功率器件的零电压开通。介绍了电路拓扑及调制方法,进行了阶段分析,并推导出了零电压开关条件。最后在一台50 kVA的绝缘栅双极型晶体管IGBT(insulated gate bipolar transistor)实验样机进行了验证。

Simulation of grid tracking control of power system connection and maximum power brushless doubly-fed generator in point wind

In this paper, based on the analysis of the mathematical model in a common synchronous reference frame of the brushless doubly-fed generator （BDFG）, the grid connection strategy and maximum energy extraction control were both analyzed. Besides, the transient simula- tion of no-load model and generation model of the BDFG have been developed on the MATLAB/Simulink platform. The test results during cutting-in grid confirmed the good dynamic performance of grid synchronization and effective power control approach for the BDFG-based variable speed wind turbines.

PID-type Terminal Sliding Mode Control for Permanent Magnet Synchronous Generator-based Enhanced Wind Energy Conversion Systems

The provision of wind farm(WF)grid codes(GCs)has become imperative for sustained grid operations,especially for WFs with permanent-magnet synchronous generator(PMSG)wind energy conversion system.Numerous techniques have been developed for executing GC requirements in the event of grid faults.Among the methods,an intriguing strategy is to enhance the performance of back-to-back(BTB)converter controllers.In this research,the PID-type terminal sliding mode control(PID-TSMC)scheme is implemented for both machine-side and grid-side converter-modified controllers of BTB-converter,to reinforce the nonlinear relationship among the state-variable and the control input.The application of this control scheme decreases the response time and improves the robustness of the BTB-converter controllers regarding uncertainty of parameters and external disturbances.The grid-side converter tracks the maximum power point,contributing to the rapid decrease of generator active power output during faults.This frees up converter capacity for injecting GC-compliant reactive current into the grid.Besides,the machine-side converter regulates DC-link voltage,in which its variations during external disturbances decrease substantially with the PID-TSMC.The discussions on the simulations contemplate on the robustness and efficiency of the implemented PID-TSMC strategy in comparison to other BTB-converter control strategies.

Super twisting sliding mode approach applied to voltage orientated control of a stand-alone induction generator

To enhance the robustness and dynamic performance of a self-excited induction generator (SEIG) used in a stand-alone wind energy system (WES), a virtual flux oriented control (VFOC) based on nonlinear super-twisting sliding mode control (STSMC) is adopted. STSMC is used to replace the conventional proportional-integral-Fuzzy Logic Controller (PI-FLC) of the inner current control loops. The combination of the proposed control strategy with space vector modulation (SVM) applied to a PWM rectifier brings many advantages such as reduction in harmonics, and precise and rapid tracking of the references. The performance of the proposed control technique (STSMC-VFOC-SVM) is verified through simulations and compared with the traditional technique (PI-FLC-VFOC-SVM). It shows that the proposed method improves the dynamics of the system with reduced current harmonics. In addition, the use of a virtual flux estimator instead of a phase-locked loop (PLL) eliminates the line voltage sensors and thus increases the reliability of the system.

应用矢量正交分解法计算背靠背换流站中氧化锌非线性电阻片有功电流的方法

阐述了S.Fryze功率理论,将金属氧化物避雷器泄漏电流分解为相互正交的有功分量与无功分量,研究了半波、全波、换流阀侧、换流桥侧、换流器侧等5种典型电压作用下金属氧化物避雷器有功电流的计算方法。