An Adaptive Control Strategy for Energy Storage Interface Converter Based on Analogous Virtual Synchronous Generator

In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To address this issue,the application of a virtual synchronous generator(VSG)in grid-connected inverters control is referenced and proposes a control strategy called the analogous virtual synchronous generator(AVSG)control strategy for the interface DC/DC converter of the battery in the microgrid.Besides,a flexible parameter adaptive control method is introduced to further enhance the inertial behavior of the AVSG control.Firstly,a theoretical analysis is conducted on the various components of the DC microgrid,the structure of analogous virtual synchronous generator,and the control structure’s main parameters related to the DC microgrid’s inertial behavior.Secondly,the voltage change rate tracking coefficient is introduced to adjust the change of the virtual capacitance and damping coefficient flexibility,which further strengthens the inertia trend of the DC microgrid.Additionally,a small-signal modeling approach is used to analyze the approximate range of the AVSG’s main parameters ensuring system stability.Finally,conduct a simulation analysis by building the model of the DC microgrid system with photovoltaic(PV)and battery energy storage(BES)in MATLAB/Simulink.Simulation results from different scenarios have verified that the AVSG control introduces fixed inertia and damping into the droop control of the battery,resulting in a certain level of inertia enhancement.Furthermore,the additional adaptive control strategy built upon the AVSG control provides better and flexible inertial support for the DC microgrid,further enhances the stability of the DC bus voltage,and has a more positive impact on the battery performance.

An Integrated Control Strategy Adopting Droop Control with Virtual Inductance in Microgrid

As there exists sorts of distributed generators in microgrid, an integrated control strategy containing different control methods against corresponding generators should be applied. The strategy in this paper involves PQ control and droop control methods. The former aims at letting generators like PV output maximum power. The latter stems from inverter parallel technique and applies to controlling generators which can keep the network voltage steady to make the parallel system reach the minimum circulation point. Due to the unworthiness of droop control applied in low-voltage microgrid of which the impedance ratio is rather high, the paper adopts the droop control introducing virtual generator and virtual impedance. Based on theoretical analysis, simulation in Matlab is also implemented to verify the feasibility of the strategy.

Research on the Impacts of the Inertia and Droop Control Gains from a Variable-Speed Wind Turbine Generator on the Frequency Response

System frequency must be kept very close to its nominal range to ensure the stability of an electric power grid.Excessive system frequency variations are able to result in load shedding,frequency instability,and even generator damage.With increasing wind power penetration,there is rising concern about the reduction in inertia response and primary frequency control in the electric power grid.Converter-based wind generation is capable of providing inertia response and primary frequency response;nevertheless,the primary frequency and inertia responses of wind generation are different from those of conventional synchronous fleets;it is not completely understood how the primary frequency and inertia responses affect the given system under various disturbances and available kinetic energy levels.Simulations are used to investigate the influences of inertia and droop control strategies on the dynamic frequency responses,particularly the index of the second frequency drop under various disturbance and wind conditions.A quantitative analysis provides insight into setting of inertia and droop control coefficients for various wind and disturbance conditions to facilitate adequate dynamic frequency responses during frequency events.

Design of Power System Stabilizer for DFIG-based Wind Energy Integrated Power Systems Under Combined Influence of PLL and Virtual Inertia Controller

Wind energy systems (WESs) based on doubly-fed induction generators (DFIGs) have enormous potential for meeting the future demands related to clean energy. Due to the low inertia and intermittency of power injection, a WES is equipped with a virtual inertial controller (VIC) to support the system during a frequency deviation event. The frequency deviation measured by a phase locked loop (PLL) installed on a point of common coupling (PCC) bus is the input signal to the VIC. However, a VIC with an improper inertial gain could deteriorate the damping of the power system, which may lead to instability. To address this issue, a mathematical formulation for calculating the synchronizing and damping torque coefficients of a WES-integrated single-machine infinite bus (SMIB) system while considering PLL and VIC dynamics is proposed in this paper. In addition, a power system stabilizer (PSS) is designed for wind energy integrated power systems to enhance electromechanical oscillation damping. A small-signal stability assessment is performed using the infinite bus connected to a synchronous generator of higher-order dynamics integrated with a VIC-equipped WES. Finally, the performance and robustness of the proposed PSS is demonstrated through time-domain simulation in SMIB and nine-bus test systems integrated with WES under several case studies.

Virtual Synchronous Generator Based Current Synchronous Detection Scheme for a Virtual Inertia Emulation in SmartGrids

Renewable energy sources, such as photovoltaic wind turbines, and wave power converters, use power converters to connect to the grid which causes a loss in rotational inertia. The attempt to meet the increasing energy demand means that the interest for the integration of renewable energy sources in the existing power system is growing, but such integration poses challenges to the operating stability. Power converters play a major role in the evolution of power system towards SmartGrids, by regulating as virtual synchronous generators. The concept of virtual synchronous generators requires an energy storage system with power converters to emulate virtual inertia similar to the dynamics of traditional synchronous generators. In this paper, a dynamic droop control for the estimation of fundamental reference sources is implemented in the control loop of the converter, including active and reactive power components acting as a mechanical input to the virtual synchronous generator and the virtual excitation controller. An inertia coefficient and a droop coefficient are implemented in the control loop. The proposed controller uses a current synchronous detection scheme to emulate a virtual inertia from the virtual synchronous generators. In this study, a wave energy converter as the power source is used and a power management of virtual synchronous generators to control the frequency deviation and the terminal voltage is implemented. The dynamic control scheme based on a current synchronous detection scheme is presented in detail with a power management control. Finally, we carried out numerical simulations and verified the scheme through the experimental results in a microgrid structure.

风电虚拟惯量延时的影响机理模型解析及替代性研究

风电机组采用虚拟惯量参与电网调频时,其本质是带延时的快速功率响应,但虚拟惯量延时对频率控制的非线性影响尚不清晰。同时,虚拟惯量存在测频精度要求高、延时大、频率微分环节放大量测误差等固有缺陷。为此,提出了风电机组虚拟惯量延时的影响机理模型解析及替代性研究的思路。首先,通过将风电机组虚拟惯量和下垂控制的延时特性近似等效为一阶惯性环节,建立风电调频使用虚拟惯量和下垂控制的系统频率响应模型;其次,基于劳斯近似法对高阶模型进行降阶解析,求得系统频率最低点的解析表达式;然后,解析求解风电调频仅使用下垂控制的系统频率响应模型,并在频率最低点指标下给出与虚拟惯量和下垂控制相同调频效果的下垂控制系数设定方法。进一步,在设定下垂控制参数下,对比两种控制方式下的最大频率变化率、稳态频率等关键指标关系,得出结论:适当改变下垂系数可替代带延时虚拟惯量,并能取得比虚拟惯量和下垂控制更佳的调频效果。最后,建立仿真模型,并从系统频率响应动态、调频能量需求、风电机组响应功率等方面验证了分析的正确性。

可再生能源高渗透下时滞孤岛微电网的负荷频率控制

针对孤岛微电网系统中大规模接入可再生能源导致的低惯性和开放通信网络中通信延迟对系统稳定运行造成的不可忽略的影响,该文研究变时滞影响下低惯性孤岛微电网系统的负荷频率控制问题。首先,提出一种引入虚拟惯性控制的时滞微电网分层频率控制模型;然后构造一个新的Lyapunov-Krasovskii泛函,它包括时滞乘积项和增广的s-dependent积分项。进而,选取复合松弛积分不等式、二次函数不等式和凸组合等方法与所构造泛函有效配合,得到保守性更低的稳定性判据。最后,通过不同场景的仿真分析验证所提方法在提高孤岛微电网时滞稳定裕度和系统动态性能方面具有更好的效果,并分析了时滞稳定裕度与控制器参数、非线性负载扰动之间的关系。

Fractional-order Virtual Inertia Control and Parameter Tuning for Energy-storage System in Low-inertia Power Grid

As conventional synchronous generators are replaced by large-scale converter-interfaced renewa-ble-energy sources(RESs),the electric power grid en-counters the challenge of low rotational inertia.Conse-quently,system frequency deviation is exacerbated and system instability may occur when the frequency deviates beyond the acceptable range.To mitigate this effect,this study proposes a virtual inertia control(VIC)strategy based on a fractional-order derivative and controller parameter-tuning method.The tuning method uses the stability boundary locus and provides a stability criterion for identifying the stability region in the parameter space.The controller parameters are then optimized within the identified stability region to suppress frequency deviation and enhance system robustness.The proposed controller and tuning method is applied to a battery energy-storage system(BESS)in a low-inertia power system with the integration of RESs.Time-domain simulations are carried out to verify the stability region and compare the per-formance of the optimized proposed controller to that of the traditional integral-order controller.The simulation results show that the stability-analysis method is effective and that the fractional-order VIC,tuned with the pro-posed method,outperforms the traditional method in both frequency-regulation performance and parametric robustness.Index Terms—Virtual inertia control,frequency regu-lation,fractional-order controller,stability region,pa-rameter tuning.

计及工作点偏移的减载风电系统频率响应模型

随着风电并网容量不断升高,利用减载风电机组参与一次调频对保障系统频率稳定性具有重要意义。然而,风机的工作点会随其转速变化而发生偏移,使得风机的实际一次调频贡献小于期望值。为此,文中首先分析了频率故障后风电机组减载功率跟踪控制与综合惯量控制的交互影响,指出了风机工作点偏移导致其调频效果削弱的基本原理。其次,基于风机的转子运动方程推导了风电功频传递函数,建立了计及减载风电机组工作点偏移的系统频率响应模型,并利用最小二乘法对其进行降阶,推导了系统频率最低点的解析式。然后,针对虚拟惯量控制的频率恢复期间引起功率倒流、微分环节放大噪声等缺点,提出利用下垂控制替代综合惯量控制。同时,为使减载风电机组获得期望的调频效果,基于频率最低点和稳态频率指标对风机控制参数进行了修正,提出了两种等效下垂系数的计算方法。最后,在MATLAB/Simulink平台建立了四机两区域模型,验证了所提降阶方法及修正方法的有效性。

基于NSGA-Ⅱ的飞轮-火电联合二次调频最优负荷分配策略

为了在提升飞轮-火电联合二次调频性能的同时控制调频成本、减少飞轮损耗,面向飞轮-火电联合系统,提出一种考虑自动发电控制(AGC)指令及电网频率偏差的基于多目标遗传算法的负荷分配策略。该策略以电网调频偏差、飞轮-火电出力能量和、飞轮损耗为三层最小化目标,考虑火电机组爬坡率及其负荷备用、飞轮荷电状态及其功率等约束条件,基于改进的非支配排序遗传算法(NSGA-Ⅱ),通过AGC功率指令变化速度及频率偏差动态调整飞轮与火电出力权重系数,以频率偏差及其变化方向调整飞轮虚拟下垂、惯性系数,求解飞轮-火电出力比例、飞轮下垂系数和飞轮惯性系数。结合中国宁夏某电厂飞轮储能系统辅助火电机组调频现场AGC指令等历史数据,在双区域两机系统模型上进行仿真实验,结果表明该负荷分配策略有效地减小了火电二次调频偏差和调节时间,提升了调频性能,同时也有效地控制了系统出力能量及飞轮损耗。

含减载控制和虚拟惯量控制的直驱风电场等值建模方法

为建立准确的具有主动支撑能力的直驱风电场等值模型,提出一种含减载控制和虚拟惯量控制的直驱风电场等值建模方法。首先,建立包含减载控制和虚拟惯量控制的直驱风机并网系统模型;其次,依据适应性分析选取转速、减载系数、惯性系数和阻尼系数作为分群指标;然后,基于分群指标利用改进K-means算法对直驱风电场中的机组进行聚类分群,得到直驱风电场的等值模型;最后,利用实际算例在不同场景下进行仿真和计算,对等值建模方法的准确性进行验证。

基于自适应虚拟电阻的低压微电网有功均分下垂控制策略

由于低压微电网中各分布式电源的线路阻抗不匹配,传统的下垂控制策略难以按照下垂系数合理分配有功功率。为此,提出一种无需通信的自适应虚拟电阻下垂控制方法。通过将微电网中每个分布式发电机(DG)单元输出的有功功率和电压传送给自适应虚拟电阻控制器中,在保证电压和频率稳定控制的前提下实现功率按逆变器容量比例进行精确分配。论文对改进方法的微电网逆变器进行小信号稳定性分析,以优化控制器有关控制参数。仿真和实验结果验证了所提控制方法的有效性。

考虑可再生能源接入的多端MMC交直流混合系统协调控制

模块化多电平变换器的零转动惯量特性,使其无法对交流电网的频率波动提供支撑,导致交直流混合系统的整体惯性下降,影响并网系统的动态性能与稳定性。文章将改进功率-电压下垂控制与虚拟同步机技术相结合,提出一种新型功率协调控制策略。在系统直流电压稳定的情况下,对交流电网进行频率调节,同时对各变换器间的功率进行合理分配,无需通讯系统即可建立有效的能量管理体系。与传统双闭环控制进行对比试验,结果表明,所提控制策略有效解决了系统由低惯量、欠阻尼引起的动态性能与稳定性的问题。

面向多运行模式的并网逆变器改进控制策略

为了改善新能源并网逆变器的性能并同时满足多运行模式(并网模式和孤岛模式)调节需求,设计了双重自适应系数,并基于下垂控制和虚拟同步发电机(virtual synchronous generator,VSG)控制提出了新颖的改进控制策略。该控制策略可灵活地调节惯量和阻尼以满足不同运行模式的需求。设计的双重自适应系数包括自适应协调系数和自适应惯量系数,前者可提高系统动态特性并增强适用性,后者可进一步改善功率超调和振荡问题以完全消除功率超调。所提出的改进控制策略的功率响应无超调和振荡,能够提供接近于VSG控制的惯量和阻尼特性且具有更快的响应速度,可同时满足并网模式下的功率调节需求和孤岛模式下的频率调节需求,具有更大的适用性和更优异的动态特性。最后,通过硬件在环实验验证了所提出的改进控制策略的有效性和可行性。

基于改进虚拟惯性控制的直流充电桩控制方法

直流充电桩充电速度快、效率高的优点使得电动汽车负载可以频繁投切,但其作为直流系统具有惯性小、阻尼弱的特点。为降低电动汽车负载投切对直流侧电压扰动的影响,文中提出一种基于改进虚拟惯性(virtual inertia,VI)控制的直流充电桩控制方法。首先,类比虚拟同步机(virtual synchronous machine,VSM)技术推出VI控制,赋予直流系统一定的惯性与阻尼支撑。其次,采用指令滤波反推积分滑模(command filter backstepping integral sliding mode,CFBISM)控制对VI控制进行改进,即采用积分滑模(integral sliding mode,ISM)控制优化VI控制,增强系统的鲁棒性,并采用指令滤波反推控制对其中关键参数进行重构,避免控制器出现计算膨胀现象,同时对电流内环采用改进ISM控制从而进一步提升控制效果。然后,通过Lyapunov稳定性判据证明所提控制方法的稳定性。最后,通过仿真对比验证了文中所提控制方法可将直流侧电压波动限制在2 V以内,动态响应速度提高约0.1 s,关键参数在稳态时的扰动限制在1 V左右,从而验证了其响应速度快、鲁棒性好的特性。

基于滑模变结构的混合微电网接口变换器双向下垂控制

由于混合微电网中的交直流子网具有不同的动态特性,当系统发生负荷突变时,会在双向接口变换器(bidirectional interface converter, BIC)两侧子网间产生功率波动,使交流母线频率和直流母线电压动态响应变差,为此提出了基于分数阶滑模控制器(fractional order sliding mode controller, FOSMC)的双向下垂控制策略。将具有鲁棒性强、响应速度快和抗干扰能力强的滑模变结构控制引入到BIC的控制中,得到改进型的分数阶滑模控制器,以改善系统的暂态响应过程。通过Matlab/Simulink平台搭建了仿真模型,在多种工况下验证了该控制策略的有效性。与传统双向下垂控制相比,该控制算法可以在保证系统原有稳态特性的同时,加快整个系统的响应速度,抑制暂态过程中BIC传输功率的瞬间波动,减小功率波动对交直流子网母线的反作用,提高整个系统的动态性能和抗扰动性能。

风电并网的电压稳定性分析与研究

风能作为一种无污染的清洁能源,近些年一直受到世界各国的青睐。但随着大规模的风电场并入电网,风能的随机性和间歇性也给电网的稳定性带来了冲击,因此,研究风电并网的电压稳定性对风电并网的安全运行有着非常重要的意义。本文以双馈异步发电机为例,通过MATLAB仿真,研究虚拟惯量控制、阻尼控制对电压频率稳定性的影响。

基于虚拟同步机的风-光-储并网系统自适应功频控制策略

风-光-储系统通过虚拟同步发电机(virtual synchronous generator,VSG)并网时,其运行工况变化将引起系统功频波动。针对这一问题,提出一种VSG自适应惯量阻尼功频控制策略。首先,建立VSG的数学模型及功率小信号模型,分析虚拟参数变化对系统稳定性的影响;然后,依据系统受扰时的功角曲线分析惯量阻尼的动态特性,设计了一种分段线性调整函数,并给出参数选取原则;最后,在Matlab/simulink平台中搭建仿真模型验证。结果表明,在工况变化情况下,采用VSG自适应控制的风光储并网系统功频响应得到了改善,相比传统VSG控制具有更好的动态调节性能。

基于模型预测的直流微网多电力弹簧协同控制策略研究

针对新能源接入、负荷投切所导致的直流微电网电压质量下降与系统呈现低惯性的问题,传统惯性控制随着电网规模的扩大适应性降低,因此提出一种多直流电力弹簧(DC electric springs,DCESs)单元下的直流微网电压协同控制策略,首先采用分布式一致性算法通过稀疏通信网络交换本地信息与相邻信息,求解全局母线电压平均值,并引入积分环节提高传统通信方式的收敛性。接着考虑系统负荷投切以及源侧功率波动导致的电压突变,基于DCES中的双向全桥DC/DC变换器构建预测模型,令各DCES根据系统功率波动状态自适应求解最佳虚拟电容值,平滑直流母线电压,提升了动态响应速度,同时分析了系统电压的收敛性与稳定性。最后通过MATLAB/Simulink在随机波动负荷、实际光伏场景下从电压质量、即插即用性能、系统惯性3个方面验证了模型的有效性,所提出的控制策略在保证系统电压平稳的同时,具有更优的动态响应能力。

直驱永磁风力发电机的变系数PD虚拟惯量控制研究

传统PD虚拟惯量控制虽然能有效避免无惯量情况下频率的二次跌落问题,但应对风速变化时,传统控制方法中固定的惯性系数可能导致惯量响应中惯量的过余或不足,风机输出有功功率延时变化,影响系统频率的变化,惯量响应效果不理想。为此,在搭建PD虚拟惯量控制模型的基础上,综合考虑转子动能与风速变化对虚拟惯量调节的影响,通过当前风速与下一时刻预测风速对应的旋转动能超前算出满足系统的变微分系数,优化传统控制方法中的风机辅助功率,匹配系统适时的惯量效应,在系统频率调整方面具有更高的灵活性,同时避免了传统控制方法机械、固定的全惯量支撑,减小机组的调频压力。最后通过仿真验证了所提策略的有效性。