基于混合势函数的直流微电网群稳定性分析

直流微电网群中的恒功率负载呈现负阻抗特性,会对直流微电网群稳定性造成不利影响,因此需对直流微网群稳定性功率界限进行分析.针对此类问题,文中采用混合势函数,对含恒功率负载的直流微电网群进行大信号稳定性分析.根据子微网间连接的DC-DC变换器特性,将直流微电网群等效成子微网与受控电流源并联的形式,以此建立直流微电网群大信号...     

带CPL的直流微电网定频滑模稳定控制

恒功率负载(CPL)固有的负阻抗特性会影响直流微电网中DC/DC变换器的稳定运行,进而使直流微电网陷入不稳定状态。为此,提出了一种带CPL的直流微电网定频滑模稳定控制方法,借助非线性的定频滑模控制策略实现对DC/DC变换器环节的稳定控制,进而使直流微电网免受CPL的不稳定干扰。首先以Boost变换器为例,介绍了恒功率负载的不稳定负载阻抗效应,并推导了对应的Boost变换器离散时间模型,接着提出了基于电流模式控制的离散时间滑模控制方法,并通过额外增加一个外部电压环路确保了闭环系统的稳定性,最后借助仿真和样机实验对所提出的方案进行了验证。实验结果表明,所提出的带CPL的直流微电网定频滑模稳定控制方法可以实现启动浪涌电流限制和确保系统稳定运行,同时拥有良好的稳态性能和瞬态性能。     

基于混合储能系统的微电网母线电压控制策略

在孤岛直流微电网中,母线电压是判断其稳定性和衡量电能质量的唯一指标。针对这一现象,在孤岛直流微电网中加入了由蓄电池-超级电容组成的混合储能单元来平抑微电网系统中出现的波动功率,同时对于超级电容控制器添加了补偿电流来提升控制精度,差额功率经过低通滤波器后,高频分量经超级电容器平抑,低频分量经蓄电池平抑,对于母线电压不论是瞬时恢复还是长期的稳定性都得到了保障。试验结果表明,不论是光照强度变化还是负载功率变化,含混合储能系统的微电网母线电压都能快速恢复至额定值,无论是电能质量,还是系统稳定性都具有一定的提升。     

基于多智能体的微电网电压稳定性协调控制系统

针对传统智能优化算法在调节含分布式电源的微电网电压稳定性时不稳定、过早收敛的问题,提出一种基于多智能体的微电网电压稳定性协调控制系统。该系统采用集中式和分布式管理相结合的方式来提高微电网的电压稳定性,在监控电压稳定性指标的同时解决电压越限的问题;同时,使用配电网智能体实时监控分布式电源总控智能体和调压智能体,通过调节分布式电源智能体的有功与无功出力来调节微电网电压。在含有3个分布式电源的IEEE 33节点系统上的仿真测试结果表明,该系统能有效解决含分布式电源的微电网电压越限的问题,调节电压稳定性。     

基于混合储能的微电网控制策略研究

微电网优化配置中风光出力的随机性和波动性给微电网的并网运行造成不利影响。为了提升不可控电源出力稳定性,减小直流母线电压波动,提高并网点电能质量,针对传统PI控制的不足,提出一种动态响应速度更快、控制效果更好的自抗扰和二阶低通滤波器复合控制混合储能系统策略,并在Matlab环境下搭建微电网仿真模型。结果表明,该策略可以提高系统的动态响应性能,减小直流母线承受的电压冲击,平抑直流母线电压波动,提高并网电能质量,验证了所提出的混合储能控制策略的正确性和可行性。     

柴油发电机组-脉冲负载系统运行行为仿真

柴油发电机组-整流器供电系统是重要的移动装备电源形式,可作为重要工程的备用电源,也可作为直流微电网的重要支撑电源。脉冲负载集成了大量电力电子器件,是一类功率波动明显且切换频繁的负载形式,以含大功率收发组件的数字式雷达为代表。在脉冲负载工作过程中,线路中电流与电压呈强烈非线性,系统动态过程复杂,难以运用解析方法表示柴油发电机组内部的机电过渡过程与电磁暂态。文中建立了基于Matlab/ Simulink 的系统模型,分析了脉冲负载在不同工作模式时,柴油发电机组输出电压与频率的瞬态和稳态指标,结果表明:该模型能够较真实地反映柴油发电机组-整流器-脉冲负载系统的运行行为。     

光储直流微电网的控制策略分析及应用

本文详细分析了光储直流微电网的控制策略,由于新能源发电系统发展较晚,其工作仍然存在一定局限性。利用新能源发出的电能往往具有间歇性、波动较大等特点。当负载变化时,系统响应也较慢。针对这些问题,本文对光储直流微电网的控制策略进行研究,并且进行了仿真分析,对未来建设含分布式发电的直流配电网系统建设与大规模推广具有重要意义。     

多储能直流微电网的分布式控制分析

本文对直流微电网分布式控制的时代意义进行了简要的分析,并围绕直流微电网的内涵以及基本电网的分布式控制结构进行了集中的阐释,也针对两储能直流微电网的稳定性展开讨论。     

分布式电源结构发展趋势

分布式电源结构(DPAs)在今天的电源系统中被广泛使用。一个传统的高功率PDA包括一个前端的交流-直流(ac-dc)变换器,由它来产生一个分布式总线(典型地为48V),以及许多局部的孤立直流-直流(dc-dc)变换器,,它们向负载提供所需要的电压。低功率系统通常采用一个较低的总线电压(12V)以及非孤立的局部直流一直流变化。人们普遍认为:尽管DPAs增加了电源转换这一级,     

多电飞机电源系统的负载并联稳定性分析

对多电飞机电源系统中恒功率负载和恒电压负载并联的系统稳定性进行了分析。阐述了恒功率负载的特性及其工作原理,介绍了多电飞机电源系统中典型恒功率负载的特点。在此基础上,对不同负载并联对多电飞机电源系统稳定性的影响进行了分析,采用Brayton-moser定理,从能量的角度分析恒功率和恒电压负载并联时机载电气系统的稳定性,并给出了系统稳定性条件。仿真结果验证了所述分析方法的正确性。     

Three-step impedance criterion for small-signal stability analysis in two-stage DC distributed power systems

Small-signal stability analysis methods based on an impedance criterion originate from the minor loop gain method and are gradually utilized in two-stage DC distributed power systems. In this paper, we conclude that the impedance criterion directly dependent on output impedance Z/sub o/(s) of the source subsystem and input impedance Z/sub i/(s) of the load subsystem is possible but gives an incorrect stability analysis for systems with a regulated source subsystem. Through introducing a mapped pure impedance of the load subsystems and the preliminary system, we develop a general three-step impedance criterion, with which a correct small-signal stability analysis can be guaranteed, regardless of the type of source subsystem. Furthermore, we introduce the application of the three-step impedance criterion in two small-signal stability analysis cases and utilize it in an example system to predict the stability shift process arising from the variation on the load resistance and input voltage value.     

直流微网母线电压纹波集中补偿自寻优策略

为抑制直流微网母线电压二次纹波,文中提出了一种直流有源滤波器集中补偿自寻优策略。在双向DC/DC变换器电压/电流双闭环控制的基础上,加入直流母线电压纹波控制,通过引入带通滤波器消除了传统控制方法中采用低通滤波器提取纹波时所产生的相位滞后问题。采用迭代自寻优方法获取重要控制参数阻抗系数K,实现直流有源滤波器对直流母线电压纹波变化的实时跟踪和集中补偿。在MATLAB/Simulink中搭建了含互联接口变流器、分布式电源、直流负荷、由DC/AC变流器接入的交流负荷以及直流有源滤波器的直流微网模型,建立了相应的实验平台。仿真和实验结果均验证了所提控制策略的有效性。     

Impedance specifications for stable DC distributed power systems

In a DC distributed power system, the interaction between individually designed power modules/subsystems may cause the instability of the whole system. In a small-signal sense, system level stability is determined by the impedance ratio Z_o/Z_i. Here, Z _o is the output impedance of the source module/subsystem, and Z_i is the input impedance of the load module/subsystem. As a result, an effective way to prevent system instability is defining impedance specifications for modules/subsystems. This paper briefly summarizes existing works and introduces the authors' contribution in defining impedance specifications. A new forbidden region for impedance ratio Z_o/Z_i on the S-plane is proposed as the system stability margin requirement. Based on this proposed forbidden region, the impedance specifications of individual loads are established. Further, a very practical measurement approach is developed to examine whether or not the system stability margin requirement of the forbidden region is satisfied     

DC bus voltage control for a distributed power system

This paper addresses voltage control of distributed DC power systems. DC power systems have been discussed as a result of the introduction of renewable, small-scale power generation units. Also, telecommunication power systems featuring UPS properties might benefit from a broader introduction of DC power systems. Droop control is utilized to distribute the load between the source converters. In order to make the loading of the source converters equal, in per unit, the voltage control algorithm for each converter has to be designed to act similar. The DC side capacitor of each converter, needed for filtering, is also determined as a consequence. The root locus is investigated for varying DC bus impedance. It is found that the risk of entering converter over-modulation is a stronger limitation than stability, at least for reasonable DC bus cable parameters. The stationary and dynamic properties during load variations are also investigated.     

Stability margin monitoring for DC distributed power systems via perturbation approaches

In multi-module power electronics systems, especially DC distributed power systems, the small-signal stability issues are often dealt with by employing Middlebrook's impedance criterion. However, for on-line system stability margin monitoring, directly measuring impedance of the source and load subsystems then making quantitative comparisons is too complicated and difficult. This paper proposes practical and simple methods, which involve applying current or voltage perturbation to the dc side of distributed power systems then only measuring the amplitude of two currents or voltages in order to monitor the stability margin. For both methods (current perturbation and voltage perturbation), an implementation approach that does not employ external voltage or current perturbation source is also presented. All these methods and approaches are equivalent to the impedance measuring and comparing method based on the impedance criterion with different forbidden regions. A comparative evaluation of each method and its corresponding implementation approach is provided.     

Realization of Parasitics in Stability of DC–DC Converters Loaded by Constant Power Loads in Advanced Multiconverter Automotive Systems

Distributed DC power systems are becoming increasingly common in advanced automotive systems. Constant power load (CPL) behavior of tightly regulated DC-DC converters in multiconverter power systems is equivalent to the dynamic negative impedance, destabilizing the DC bus and, consequently, the system. Various techniques have been developed to control ideal/lossless converters loaded by CPLs. Loss components significantly enhance the stability of the cascaded converters. In this paper, the effects of parasitics in the behavior of DC-DC converters loaded by CPLs are investigated. Furthermore, the stability of power converters loaded by CPLs in parallel to conventional constant voltage loads in the presence of loss components is analyzed. Design criteria are presented for converter operation in continuous and discontinuous conduction modes, which gives recommendations on the design of multiconverter DC power systems to avoid negative impedance instability. The proposed stable operation criteria are validated with hardware prototypes and simulation analyses.     

Nonlinear-controlled strategy for soft-switched series-resonant DC/AC inverter without auxiliary switches

A nonlinear control for soft-switched series-resonant DC/AC inverter without auxiliary switches is presented. The inverter is configured by a full-bridge series-resonant inversion (FB-SRI) without cycloconversion and auxiliary switches. The inverter is a series resonator with four main switches to configure adaptively the output current suitable for impedance load. The output sinusoidal voltage is synthesized by a series of equal-amplitude quasisinusoidal pulses (QSPs) and the corresponding current is formed by unequal QSPs and adaptively phase-shifts to the impedance load. The nonlinear control strategy is designed against the input DC perturbation and achieves good dynamic regulation. The presented FB-SRI is operated by frequency modulation with a constant-on time control. Waveform syntheses for the output sinusoidal voltage and its current are clearly derived. A typical design example of a 500W FB-SRI inverter is examined to assess the system performance. The power efficiency is over 90% when the inverter output is above 200 W. The total harmonic distortions (THDs) for various impedance loads are all within 6%.     

直流微电网双向AC/DC变换器鲁棒前馈控制策略研究

针对双向AC/DC功率变换器在直流微电网母线电压稳定性方面的问题,文中提出了一种结合LESO和滑模理论的前馈鲁棒控制策略。通过建立直流微电网三相AC/DC双向功率变换器的动态数学模型,架构了三阶线性扩张状态观测器,并将三阶LESO的观测值用于滑模控制器的设计。该控制策略能够在不需要额外电流传感器的情况下实现前馈控制,并确保系统具有良好的动态性能。该策略还能够有效降低滑模控制的实现难度,提高系统的鲁棒性。仿真分析验证了文中所提控制策略的有效性。     

A series-resonant DC/AC inverter for impedance-load drives

A DC/AC inverter without cycloconversion configured by a half-bridge series-resonant inversion (HB-SRI) circuit is presented. The inverter is a series resonator with two auxiliary switches in shunt with the resonant capacitor so as to configure adaptively the output current suitable for impedance load. The output sinusoidal voltage is synthesized by a series of equal-amplitude quasisinusoidal pulses (QSPs) and the corresponding current is formed by unequal QSPs and adaptively phase-shifts to the impedance load. The presented HB-SRI is operated by frequency modulation with a constant-on time control. System modeling and waveform syntheses for the output sinusoidal voltage and its current are clearly derived, A typical design example of a 500 W HB-SRI inverter is examined to assess the system performance. The power efficiency is over 90% when the inverter output is above 200 W. The total harmonic distortions (THDs) for various impedance loads are all within 6%