Frequency Control of Power System with Renewable Power Sources by HVDC Interconnection Line and Battery Considering Energy Balancing

Recently, introduction of renewable energy sources like wind power generation and photovoltaic power generation has been increasing from the viewpoint of environmental problems. However, renewable energy power supplies have unstable output due to the influence of weather conditions such as wind speed variations, which may cause fluctuations of voltage and frequency in the power system. This paper proposes fuzzy PD based virtual inertia control system to decrease frequency fluctuations in power system caused by fluctuating output of renewable energy sources. The proposed new method is based on the coordinated control of HVDC interconnection line and battery, and energy balancing control is also incorporated in it. Finally, it is concluded that the proposed system is very effective for suppressing the frequency fluctuations of the power system due to the large-scale wind power generation and solar power generation and also for keeping the energy balancing in the HVDC transmission line.

Frequency Control of Power System with Solar and Wind Power Stations by Using Frequency Band Control and Deadband Control of HVDC Interconnection Line

In recent years, environmental problems are becoming serious and renewable energy has attracted attention as their solutions. However, the electricity generation using the renewable energy has a demerit that the output becomes unstable because of intermittent characteristics, such as variations of wind speed or solar radiation intensity. Frequency fluctuations due to the installation of large scale wind farm (WF) and photovoltaics (PV) into the power system is a major concern. In order to solve the problem, this paper proposes two control methods using High Voltage Direct Current (HVDC) interconnection line to suppress the frequency fluctuations due to large scale of WF and PV. Comparative analysis between these two control methods is presented in this paper. One proposed method is a frequency control using a notch filter, and the other is using a deadband. Validity of the proposed methods is verified through simulation analyses, which is performed on a multi-machine power system model.

High-frequency Resonance Analysis and Impedance Reshaping Control of MMC-HVDC System Based on Frequency Coupling Impedance Model

In recent years, high-frequency resonance (HFR) events occurred in several modular multilevel converter based high-voltage direct current (MMC-HVDC) projects. The time delay of an MMC-HVDC system is the critical factor that induces HFR. The frequency coupling affects the impedance characteristics of an MMC and further deteriorates system stability. Therefore, in this paper, a multi-input multi-output admittance model of an MMC-HVDC system is developed to analyze its frequency characteristics. The effects of current loop, power loop, phase-locked loop, and operating point on the MMC frequency coupling degree are analyzed in detail. Meanwhile, to further suppress HFR in the MMC-HVDC system, an enhanced impedance reshaping control strategy based on the equivalent single-input single-output impedance model is proposed. Finally, the accuracy of the enhanced impedance model and the effectiveness of the impedance reshaping control are verified by electromagnetic transient simulations in PSCAD.

Steady-state Voltage Security-constrained Optimal Frequency Control for Weak HVDC Sending-end AC Power Systems

Due to the fact that a high share of renewable energy sources(RESs)are connected to high-voltage direct current(HVDC)sending-end AC power systems,the voltage and frequency regulation capabilities of HVDC sending-end AC power systems have diminished.This has resulted in potential system operating problems such as overvoltage and overfrequency,which occur simultaneously when block faults exist in the HVDC link.In this study,a steady-state voltage security-constrained optimal frequency control method for weak HVDC sending-end AC power systems is proposed.The integrated virtual inertia control of RESs is employed for system frequency regulation.Additional dynamic reactive power compensation devices are utilized to control the voltage of all nodes meet voltage security constraints.Then,an optimization model that simultaneously considers the frequency and steady-state voltage security constraints for weak HVDC sending-end AC power systems is established.The optimal control scheme with the minimum total cost of generation tripping and additional dynamic reactive power compensation required is obtained through the optimization solution.Simulations are conducted on a modified IEEE 9-bus test system and practical Qing-Yu line commutated converter based HVDC(LCC-HVDC)sending-end AC power system to verify the effectiveness of the proposed method.

高频链矩阵变换器直接功率反步控制策略

针对高频链矩阵变换器(HFLMC)电路前后级耦合导致系统动态性能和鲁棒性降低的问题,提出一种基于直接功率的非线性反步控制策略(BS-DPC)。首先,建立HFLMC非线性数学模型和有功、无功功率动态模型,分析双极性电流空间矢量调制策略;然后,在考虑系统不确定性情况下引入2个解耦控制分量,设计直流输出电流和无功功率反步控制器,实现电池不同工况下输出电流参考值的快速跟踪控制;最后,根据李雅普诺夫稳定性理论证明HFLMC闭环系统全局渐进稳定性,并对比传统PI直接功率控制和BS-DPC策略。仿真和实验结果表明,所提BS-DPC策略控制HFLMC提高了输出电流的动态性能和电网波动及直流滤波电感变化下的鲁棒性,响应时间减少了约78%,网侧THD降低了0.98%。

多分区异步互联电力系统频率稳定分析与控制研究综述

随着可再生能源装机的快速增长,以及电网由大同步电网向多分区异步互联电网的架构转变,使得分区电网逐步呈现“低惯量+调频资源匮乏”的特性,频率安全问题日益凸显。利用高压直流输电系统(high voltage direct current,HVDC)的快速功率控制能力可实现对异步互联分区电网之间调频资源的共享,抑制大频率扰动后的频率变化率及频率极值点,提升异步互联电网的频率稳定性。首先,介绍了国内外基于直流系统的调频控制方法以及直流参与调频后异步互联系统频率稳定分析的研究现状。然后,详细阐述了基于电网换相换流器和基于电压源型换流器两种类型HVDC频率控制方法的基本原理,以及HVDC参与频率支撑后异步互联系统的频率稳定分析方法。最后,对多分区异步互联系统频率稳定分析和直流调频控制目前存在的问题以及未来发展方向进行了总结和归纳。

Compensation Control and Parameters Design for High Frequency Resonance Suppression of MMC-HVDC System

Large time delay is one of the inherent features of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system and is the main factor leading to the unfavorable’negative resistance and inductance’characteristic of MMC impedance.Research indicates that this characteristic interacting with the capacitive characteristics of an AC system is the cause of high frequency resonance(HFR)in the Yu-E HVDC project.As the current controller is one of the main factors that affects the MMC impedance,a compensation control to imitate the paralleled impedance at the point of common coupling(PCC)is proposed.Therefore,the structure and parameter design of the compensation controller are core to realizing HFR suppression.There are two potentially risky frequency ranges of HFRs(around 700 Hz and 1.8 kHz)in the studied AC system within 2.0 kHz.The core concept of HFR suppression is to make the phase angle of MMC impedance smaller than 90◦in the two risky frequency ranges according to impedance stability theory.Hence,the design parameters aim to coordinate the phase angle of MMC impedance in the two risky frequency ranges.In this paper,three types of compensation controller are studied to suppress HFRs,namely,first-order low pass filter(LPF),second-order LPF,and third-order band pass filter.The results of parameter design show that the first-order LPF cannot suppress both HFRs simultaneously.The second-order LPF can suppress both HFRs,however,it introduces a DC component into the current control loop.Therefore,a high pass filter is added to form the recommended third-order controller.All parameter ranges of the compensation controller are derived using analytical expressions.Finally,the correctness of the parameter design is proofed using time-domain simulations.

Frequency Regulation of VSC-MTDC System with Offshore Wind Farms

Frequency regulation of voltage source converter-based multi-terminal high-voltage direct current(VSC-MTDC)system with offshore wind farms enhances the frequency stability by compensating the power for a disturbed AC system.However,it is difficult to reasonably allocate frequency-regulation resources due to a lack of coordination mechanisms between wind farms and the MTDC system.Moreover,it is difficult for the frequency control of the wind farms to manage changes in wind speed;and the risk of wind-turbine stalls is high.Thus,based on the kinetic energy of wind turbines and the power margin of the converters,the frequency-regulation capability of wind turbines is evaluated,and a dynamic frequency-support scheme considering the real-time frequency-support capability of the wind turbines and system frequency evolution is proposed to improve the frequency-support performance.A power adaptation technique at variable wind speeds is developed;the active power in the frequency-support stage and restoration stage is switched according to the wind speed.A hierarchical zoning frequency-regulation scheme is designed to use the frequency-regulation resources of different links in the MTDC system with wind farms.The simulation results show that the novel frequency-regulation strategy maintains frequency stability with wind-speed changes and avoids multiple frequency dips.

可调频旋转磁场仪的装置设计与磁场测量

在教学演示仪器中利用三相交流电产生旋转磁场的传统方法存在仪器损耗大、安全隐患多、成本昂贵等问题。本论文设计了一种可调频旋转磁场的产生装置,在四个辐射状横放的带铁芯螺线管中通入低压直流电,通过PLC板编程对电流进行换向,同时改变换向时间可使置入装置中心的小磁针的偏转周期发生变化,从而达到可调频的效果。螺线管中通入单相恒定直流电时,小磁针不发生偏转;通入双相矩形脉冲电流时,小磁针以45°角步进旋转。磁场方向的转速取决于电流的换向频率。该装置不仅规避了传统方法的不足,且同时兼具定性演示和定量测量双重功能,可作为一款性能优异的实验教学仪器。

Secondary Frequency Control Considering Optimized Power Support From Virtual Power Plant Containing Aluminum Smelter Loads Through VSC-HVDC Link

The growing number of renewable energy replacing conventional generators results in a loss of the reserve for frequency control in power systems,while many industrial power grids often have excess energy supply due to abundant wind and solar energy resources.This paper proposes a secondary frequency control(SFC)strategy that allows industrial power grids to provide emergency high-voltage direct current(HVDC)power support(EDCPS)for emergency to a system requiring power support through a voltage source converter(VSC)HVDC link.An architecture including multiple model predictive control(MPC)controllers with periodic communication is designed to simultaneously obtain optimized EDCPS capacity and minimize adverse effects on the providing power support(PPS)system.Moreover,a model of a virtual power plant(VPP)containing aluminum smelter loads(ASLs)and a high penetration of wind power is established for the PPS system.The flexibility and controllability of the VPP are improved by the demand response of the ASLs.The uncertainty associated with wind power is considered by chance constraints.The effectiveness of the proposed strategy is verified by simulation results using the data of an actual industrial power grid in Inner Mongolia,China.The DC voltage of the VSCs and the DC in the potlines of the ASLs are also investigated in the simulation.

基于改进基频调制电流源换流器的高压直流输电系统

主动换相型电流源换流器(current source converter,CSC)是一种新型的电流源换流器,其具有功率密度高,控制灵活,且无换相失败风险等优点,在直流输电领域具有广阔的应用前景。采用脉冲宽度调制的CSC存在直流电压波动大,开关损耗高等问题,不适用于直流输电场景。基频调制的CSC虽然缓解了直流电压波动,但是其仅有一个控制自由度,无法实现有功无功独立控制。针对上述问题,在基频调制CSC的基础上,提出一种适用于高压直流输电的改进型基频调制电流源换流器。首先分析改进基频调制原理和换流器交直流侧谐波特性,并设计直流滤波器;然后,建立系统的数学模型,并提出相应的系统功率控制策略;同时考虑到系统需要向无源网络供电的情况,提出一种无源网络供电控制策略。最后在PSCAD/EMTDC中搭建仿真模型,验证所提调制方法和控制策略的正确性和有效性。

功率阶跃型LCC-HVDC频率支撑控制策略

随着大量常规机组被直流馈入和新能源发电替代,系统惯量水平下降,调频资源减少,频率稳定性问题日益突出。基于电网换相型换流器的直流输电(line-commutatedconverterbasedhigh-voltagedirect-current,LCC-HVDC)应用广泛,利用其功率快速调节能力为系统提供支撑是改善频率稳定性问题的有效手段。该文基于功率阶跃型频率控制的基本框架,考虑LCC的出力限制,以出现功率缺额后频率最低点最高为目标建立了LCC-HVDC系统的出力时序优化模型。基于序列二次规划法对优化问题进行求解,确定最佳的LCC附加功率与支撑时间。基于MATLAB/Simulink的仿真验证了所提频率支撑控制策略的有效性。

高压直流输电系统孤岛运行调频策略

高压直流输电系统采用送端孤岛运行方式能够显著改善远距离送电系统稳定性和提升送电能力,其中孤岛系统的频率稳定性是决定能否孤岛运行的关键因素之一。结合前期天广、云广直流孤岛调试结果,阐明孤岛方式下优先利用直流系统频率限制器(frequency limitation control,FLC)平衡功率波动、放大机组一次调频死区作为后备措施、优先调整机组功率、利用FLC自动跟随的调频策略。针对孤岛方式下直流双极跳闸后出现的部分机组调相运行的现象,利用电力系统功率扰动的3阶段分配原理解释了产生原因,提出避免机组长时间调相运行的控制策略。现场试验结果验证了所提调频策略的有效性,为未来直流孤岛运行方式安排和控制措施的确定提供了依据。

基于空间矢量双滞环策略的STATCOM直接电流控制方法

提出一种适用于STATCOM的直接电流控制新方法以减小开关频率和电流跟踪误差。该方法通过指令电流求导矩阵替代参考电压预测方法,能够准确判定参考电压矢量的位置,并根据误差电流矢量与双滞环阈值的大小选择优化的开关状态输出。与其它电流控制方法相比,基于空间矢量双滞环策略的直接电流控制方法可以保证无功电流的快速响应性能,同时有效降低开关频率。仿真与实验结果证明其良好的动静态性能。

考虑频变参数和直流控制的直流输电系统线路故障解析

提出了考虑频变参数和直流控制的直流输电系统线路故障时域解析方法,为直流线路故障分析与故障检测提供了解析基础和实用工具。首先,建立了直流输电系统线路故障的复频域模型,推导了故障电气量的复频域表达式。继而,根据故障行波沿直流线路的传播规律,提出了频变参数的惯性等值模型;根据直流线路故障后直流控制系统的动作规律,提出了直流控制的比例—积分等值模型。进一步,基于频变参数和直流控制等值模型,对复频域故障电气量进行拉氏反变换得到时域表达式,并对解析结果与EMTDC仿真结果进行比较,相关结果验证了所提出的解析方法的有效性。最后,探讨了故障解析可能的工程应用场景,以直流线路行波保护为例进行了具体分析,分析结果表明故障解析具有良好的工程应用价值。

模块化多电平换流器效率优化控制器设计

模块化多电平换流器每相投入模块的电压总和不平衡时,会导致三相桥臂之间出现以2倍频负序性质为主的环流。为此,设计了一种效率优化控制器。模块化多电平换流器模块化的特点使得电容电压排序算法成为一种非常好的均衡控制方法。在研究了模块化多电平换流器数学模型的基础上,利用2倍频负序dq旋转坐标变换,设计了环流解耦抑制控制器,并结合电容电压优化排序算法,得到对应的各个子模块的触发脉冲。仿真结果表明,所设计的控制系统不仅能够降低器件的开关频率,而且相间环流也得到了很好的抑制,因此降低了系统运行损耗,提高了系统运行效率。

三相电压型PWM整流器准定频直接功率控制

建立三相电压型脉宽调制(pulse width modulation,PWM)整流器在不同坐标系下的数学模型,分析直接功率控制(direct power control,DPC)的工作原理。针对直接功率控制中开关频率变化问题,通过对PWM整流器瞬时功率分析推导,提出一种内环直接采用电流控制的新型准定频直接功率控制策略。仿真验证了算法的可行性。采用PM300DVA120智能功率模块,设计50 kVA的三相电压型PWM整流器控制实验,在10 kHz、5μs的开关频率下获得良好的实验结果。实验结果表明,所提方法实现单位功率因数运行,与现行的DPC-SVM定频控制方法相比,具有更好的动静态响应性能。

双向全桥DC-DC变换器基于电感电流应力的双重移相优化控制

通过分析双向全桥DC-DC变换器采用单移相和双重移相控制的工作原理,推导出了两种控制方式下变换器电感电流应力与传输功率、输入与输出电压调节比及移相角比之间的数学关系。为了有效降低变换器电流应力,针对不同的传输功率及电压调节比,通过寻优求得使电感电流应力达到最小的最优移相角。据此提出一种双向全桥DC-DC变换器双重移相优化控制策略,在实现输出电压闭环控制的同时使变换器电流应力达到最小。采用该优化控制策略,双重移相控制的电流应力始终小于单移相控制,并且当变换器工作在轻载且电压调节比较大时,该优化控制策略的优势更加突出。搭建了实验样机,对理论分析进行了验证,并与传统单移相控制进行了对比。实验结果验证了所提出最优控制策略的有效性与可行性。

HVDC附加控制策略对频率稳定性的影响研究

基于不完全微分PID控制原理设计了一种高压直流(HVDC)输电系统附加频率控制器,采用容易获得、稳定可靠、对频率稳定有很好的控制效果的直流双侧频率作为输入信号。该控制器可根据频率变化调节HVDC功率指令,当系统发生故障而导致频率上升或下降至动作频率时,HVDC将增加或减少从另一端系统吸收或输送的有功功率,来快速化解故障端系统的有功过剩或缺额情况。针对该控制器,利用PSCAD/EMTDC在两区域系统中进行了时域仿真分析,证明了所设计控制器的有效性。

适合风电接入的直流输电辅助频率控制策略

针对含规模化风电接入的交直流电力系统的频率稳定问题,以抑制风电出力大幅度随机扰动引起的频率波动为目的,提出了高压直流输电(high voltage direct current transmission,HVDC)附加频率控制(frequency control,AFC)和自动发电控制(automatic generation control,AGC)配合的辅助频率控制策略。该策略在风电出力发生大幅度随机扰动时,AFC利用HVDC功率快速调制和短时过载能力快速平衡风电出力扰动中变化较快的分量,控制器基于TLS-ESPRIT算法和改进射影控制理论设计,阶数低,易于工程实现;基于传统PI控制的AGC自动跟踪电网功率波动,调整调频机组出力平衡变化较慢的有功功率扰动分量,维持系统有功功率平衡,保持电力系统频率稳定。最后,利用PSCAD/EMTDC在改造的四机两区域模型中进行了仿真分析,结果表明所提策略充分利用了交直流电力系统的频率调节能力,能较好地抑制风电出力引起的频率波动。