不对称电压下基于NPC拓扑并网逆变器的模型预测控制研究

不对称电压暂降在电网实际运行中时有发生。该文在建立三相三电平中性点嵌位(neutral point clamped,NPC)并网逆变器数学模型基础上,提出一种电力系统发生不对称故障情况下的模型预测控制(model predictive control, MPC)方法。在预测控制方案中无需PI控制器的使用,没有相应的参数需要调节;通过在代价函数中引入附加控制项的权重系数,可有效保持三电平NPC逆变器中性点电压的平衡。最后在Matlab平台对所提控制策略进行验证。仿真结果表明:当系统发生不对称故障时,NPC并网逆变器能够更有效地抑制负序电流和功率震荡。相比于三相二电平逆变器,NPC并网逆变器在负载侧可以获得更好的电能质量。     

弱电网条件下LCL型Vienna整流器控制策略研究

针对LCL型滤波器存在固有谐振尖峰,实际电网存在变化的电网阻抗以及电网电压背景谐波的问题,基于dq同步旋转坐标系,提出弱电网条件下LCL型Vienna整流器非线性混合无源控制策略,该控制策略可保证闭环系统的渐进稳定,在理想电网和弱电网条件下均实现直流侧电压快速跟踪给定值及交流侧电流正弦化,同时能够实现所建立的系统模型中dq分量之间耦合项的消除。应用Matlab/Simulink搭建了系统仿真模块,并在理想电网条件和弱电网条件2种情况下进行了仿真试验,仿真试验验证了所提控制策略的可行性。     

级联H桥SVG控制策略研究

对于H桥级联型SVG,采用基于瞬时无功功率理论的无功电流检测法对SVG的输出电流进行检测,采用ip-iq检测法可以有效地检测电网处于平衡或不平衡条件下的无功电流。该文研究了直流侧电压控制方法,由于三相损耗的影响,SVG的直流侧电压采用分层控制,即直流侧整体电压平衡控制、各相电压平衡控制以及各相模块电压平衡控制。其中,电流内环作用于直流电,起到跟踪、补偿无功的作用,电压外环要维持直流侧的整体有功平衡。     

三电平四桥臂有源电力滤波器的预测电流控制研究

为解决三电平四桥臂结构开关矢量多、计算量大及控制复杂等问题,重点研究适用于三电平四桥臂结构的电流预测控制策略,并通过建立Matlab模型,进行理论分析和仿真研究。仿真和实验结果表明:采用预测电流控制方法的有源电力滤波器对谐波电流和中线电流有较好的补偿效果,并能有效地控制直流侧电压平衡。     

热电阻引线电阻补偿电路

一、桥式电路图1中,热电阻Rt与电桥是用两条线连接的,引线电阻与热电阻阻值之和构成一个桥臂的总电阻,引起桥路的不平衡以及测量误差。图2中,热电阻Rt用三条线与电桥相连,设三条引线电阻相等,记为r0,其中一条线置于电源回路,r上产生的微小压降并不影响桥路的平衡,另两条线分别置于桥的两臂,若r相等也不影响桥路的平衡,这样一来,零点时的输出V0仍等于零。图1桥式电阻-电压变换器摇摇摇摇摇摇图2三线制桥式电路二、双电流源线电阻补偿电路集成运算放大器与电流源搭配起来,可以组成引线电阻补偿电路。电流源可以由半导体三极管、场效应管、恒…     

双反激式微逆变器系统的控制策略与设计

针对单级反激式光伏并网微逆变器开关损耗大以及容易产生高频电压尖峰的问题,研究双级反激式有源钳位变换器。采用有源钳位电路,使逆变器在吸收漏感磁能的同时实现零电压开通。为减小输出电流纹波,双反激管通过正弦脉宽调制实现交错导通工作模式;并根据双反激变化器负载可能出现不平衡,建立微逆变系统等效数学模型和等效电路,推导硬件设计参数和计算公式。最后通过软件仿真与样机实验的对比,验证双反激式逆变器控制原理和元器件设计选择的正确性。     

一种改善逆变器输出动态响应的方法

本文提出了一种改进逆变器输出动态响应的方法,在逆变器控制器中断服务程序中,通过瞬态时刻电压电流的一些特性,判断出瞬投以及瞬卸时刻,并采取一些只在瞬态时刻有效的措施,从而达到改善瞬态时的动态响应速度,且不影响UFS稳态时的工作。经过在自制样机上试验,逆变器纯阻性负载瞬投和瞬卸时刻动态响应指标可做到6％以内。     

光伏逆变器企业如何应对光伏电站接入电网的技术要求

由于昼夜交替和天气的影响,光伏发电不可能像传统以燃料为核心能源的发电厂一样具有比较平稳的功率输出,光伏发电具有不可控性和间歇性。将太阳能转化为电网可以接受能源的核心设备是光伏并网逆变器,逆变器将直流电转换成交流电的功率电力电子器件在开通和关断过程会引起电网中谐波、三相电流不平衡、电压波动、闪变等     

UPS控制策略对比分析

随着电子技术的不断发展,使不同高级应对措施的应用即UPS电源的全数字化控制逐渐成为可能。为使系统控制性能增强,引入全数字化策略控制逆变电源。当前,UPS得到了很大的发展,趋向于全数字化、模块化、智能化等方向不断前进。对于UPS来说,其控制策略基本上涉及到逆变器与整流器两个方面的内容,在这里,前者涉及到直流供电电源等,按照电路结构的差异大体上涉及到单相半桥和全桥、三相桥式、变压器中心抽头推挽式逆变器等。另一方面,后者因桥臂输出电压有零电压续流这一种情况,能够达到倍频,在相对偏小的开关频率下能够实现非常理想的谐波控制。长期以来,波形控制技术始终属于逆变器行业的一个重要的方向,经过长期的探讨形成诸多类型的控制策略,中PID控制算法属于业界最为普及的一种技术方法。     

单相PWM直流电源直流电压波动抑制策略研究

单相PWM直流电源在广泛应用的同时,直流电压二倍频波动对一些敏感负荷提出了挑战.为抑制直流电压波动,分析二倍频波动产生原理并提出了一种二倍频抑制电路拓扑,运用PR控制器设计了电压外环电流内环的双闭环控制策略,通过有效转移输入功率中二倍频波动,从而达到有效抑制直流电压波动的目的.最后,利用Matlab/Simulink仿...     

Negative sequence compensation within fundamental positive sequence reference frame for a stiff micro-grid generation in a wind power system using slip ring induction machine

An isolated wind power generation scheme using slip ring induction machine (SRIM) is proposed. The proposed scheme maintains constant load voltage and frequency irrespective of the wind speed or load variation. The power circuit consists of two back-to-back connected inverters with a common dc link, where one inverter is directly connected to the rotor side of SRIM and the other inverter is connected to the stator side of the SRIM through LC filter. Developing a negative sequence compensation method to ensure that, even under the presence of unbalanced load, the generator experiences almost balanced three-phase current and most of the unbalanced current is directed through the stator side converter is the focus here. The SRIM controller varies the speed of the generator with variation in the wind speed to extract maximum power. The difference of the generated power and the load power is either stored in or extracted from a battery bank, which is interfaced to the common dc link through a multiphase bidirectional fly-back dc-dc converter. The SRIM control scheme, maximum power point extraction algorithm and the fly-back converter topology are incorporated from available literature. The proposed scheme is both simulated and experimentally verified.     

Feedforward simple control technique for on-chip all-digital three-phase AC/DC power-MOSFET converter with least components

A novel simple control technique for on-chip all-digital three-phase alternating current to direct current (AC/DC) power-metal oxide semiconductor field-effect transistors (MOSFET) converter with least components, which is employed to obtain small current and DC output voltage ripples as well as excellent performance, and using a feedforward simple control method for DC output voltage regulation is proposed. The proposed all-digital feedforward controller has the features of low cost, simple control, fast response, independence of load parameters and the switching frequency, it has no need for compensation, and high stability characteristics; moreover, the proposed controller consists of three operation amplifiers and few digital logic gates that are directly applied to the three-phase converter. The power-MOSFETs are also known as power switches, whose control signals are derived from the proposed all-digital feedforward controller. Instead of thyristors or diodes, the application of power-MOSFETs can reduce the loss of AC/DC converter that is proper to the power supply system. The input stage of an AC/DC converter functions as a rectifier and the output stage is a low pass inductor capacitor (LC) filter. The input AC sources may originate from miniature three-phase AC generator or low-power three-phase DC/AC inverter. The maximum output loading current is 0.8 A and the maximum DC output ripple is less than 200 mV. The prototype of the proposed AC/DC converter has been fabricated with Taiwan Semiconductor Manufacturing Company (TSMC) 0.35 mum 2P4M complementary MOS (CMOS) processes. The total chip area is 2.333 1.960 mm². The proposed AC/DC converter is suitable for the following three power systems with the low power, DC/DC converter, low-dropout linear regulator and switch capacitor. Finally, the theoretical analysis is verified to be correct by simulations and experiments.     

Simulation and performance evaluation of shunt hybrid power filter using fuzzy logic based non-linear control for power quality improvement

This paper deals with design and simulation of a three-phase shunt hybrid power filter consisting of a pair of 5th and 7th selective harmonic elimination passive power filters connected in series with a conventional active power filter with reduced kVA rating. The objective is to enhance the power quality in a distribution network feeding variety of non-linear, time-varying and unbalanced loads. The theory and modelling of the entire power circuit in terms of synchronously rotating reference frame and leading to a non-linear control scheme is presented. This work involves introduction of individual fuzzy logic controllers for d and q axis current control and for voltage regulation of the DC link capacitor. The simulation schematic covering the power and control circuits have been developed taking into account severe harmonic distortion caused by non-linear and unbalanced loads. The effectiveness of the fuzzy logic controller for the compensation of harmonics and reactive power has been verified by successive simulation runs and analysis of the results. The proposed controller is also able to compensate the distortion generated by the voltage- and current-fed non-linear loads, unbalanced and dynamically varying loads. Further, excellent regulation of the DC link voltage is accomplished, which significantly contributes to improvement of power quality.     

Three-phase power-flow by direct ZBR method for unbalanced radial distribution systems

This paper introduces a novel three-phase power flow approach for unbalanced radial distribution systems. The proposed approach is developed based on the branch frame of reference, rather than the traditional bus frame of reference. On the basis of the branch frame of reference, a simple direct iterative method can be applied. Hence, the proposed approach may be called the `direct Z _BR method'. Basic graph theory and injection current technique are also applied in the proposed approach. The clear theoretical foundation and the simple topology of the radial distribution network make the proposed method efficient and reliable. To demonstrate the better convergence performance and the efficiency of the proposed approach, four three-phase IEEE test feeders are used for comparisons. The test results show that the proposed method has robust convergence characteristics and high performance, especially for large-scale radial distribution systems.     

基于自抗扰控制的直流微电网双向Buck-Boost变换器控制策略研究

为了降低直流微电网母线电压的波动,提出基于自抗扰控制的双向Buck-Boost变换器控制策略。运用直流母线电压外环、直流变换器电感电流内环的控制方法实现直流微电网与储能系统之间的能量双向流动。进一步提出基于扩张状态观测器观测输出总扰动,包括负载电流和母线电压的变化,在负载扰动电流影响系统的直流母线电压最终输出前,主动从外环被控对象的输入信号电感电流或输出信号母线电压中提取扰动信息,然后尽快用控制信号将其消除,从而大大降低其对被控量的影响,以有效抑制暂态直流母线的电压波动和冲击,在母线电压产生波动时能够快速恢复到正常的工作状态。仿真验证表明:储能系统可以通过控制策略实现能量的双向传递,并且当母线产生功率波动和电流冲击时,储能系统可以使直流母线电压稳定,提高了系统的可靠性。     

光电平台伺服系统自抗扰滑模控制

提出一种基于参考模型的自抗扰滑模控制器,它包括一个自抗扰控制器和一个全局滑模控制器.根据参考模型,利用跟踪微分器设计自抗扰控制器,控制参考模型的输出精确跟踪指令输入信号.全局滑模控制器控制伺服系统被控对象的输出高精度跟踪参考模型的输出.光电平台伺服系统的实验结果证明该新型控制器能有效补偿系统的参数不确定性和非线性扰动,提高了伺服系统的跟踪精度.系统具有全局鲁棒性.     

A single phase photovoltaic inverter control for grid connected system

This paper presents a control scheme for single phase grid connected photovoltaic (PV) system operating under both grid connected and isolated grid mode. The control techniques include voltage and current control of grid-tie PV inverter. During grid connected mode, grid controls the amplitude and frequency of the PV inverter output voltage, and the inverter operates in a current controlled mode. The current controller for grid connected mode fulfills two requirements – namely, (i) during light load condition the excess energy generated from the PV inverter is fed to the grid and (ii) during an overload condition or in case of unfavorable atmospheric conditions the load demand is met by both PV inverter and the grid. In order to synchronize the PV inverter with the grid a dual transport delay based phase locked loop (PLL) is used. On the other hand, during isolated grid operation the PV inverter operates in voltage-controlled mode to maintain a constant amplitude and frequency of the voltage across the load. For the optimum use of the PV module, a modified P&O based maximum power point tracking (MPPT) controller is used which enables the maximum power extraction under varying irradiation and temperature conditions. The validity of the proposed system is verified through simulation as well as hardware implementation.     

Neural Network and Fuzzy Control Based 11-Level Cascaded Inverter Operation

This paper presents a combined control and modulation technique to enhance the power quality (PQ) and power reliability (PR) of a hybrid energy system (HES) through a single-phase 11-level cascaded H-bridge inverter (11-CHBI). The controller and inverter specifically regulate the HES and meet the load demand. To track optimum power, a Modified Perturb and Observe (MP&O) technique is used for HES. Ultra-capacitor (UCAP) based energy storage device and a novel current control strategy are proposed to provide additional active power support during both voltage sag and swell conditions. For an improved PQ and PR, a two-way current control strategy such as the main controller (MC) and auxiliary controller (AC) is suggested for the 11-CHBI operation. MC is used to regulate the active current component through the fuzzy controller (FC), and AC is used to regulate the dc-link voltage of CHBI through a neural network-based PI controller (ANN-PI). By tracking the reference signals from MC and AC, a novel hybrid pulse width modulation (HPWM) technique is proposed for the 11-CHBI operation. To justify and analyze the MATLAB/Simulink software-based designed model, the robust controller performance is tested through numerous steady-state and dynamic state case studies.     

Modelling and analysis of an open-loop induction motor drive incorporating the effect of inverter dead-time

The objective of this paper is to study the influence of inverter dead-time on steady as well as dynamic operation of an open-loop induction motor drive fed from a voltage source inverter (VSI). Towards this goal, this paper presents a systematic derivation of a dynamic model for an inverter-fed induction motor, incorporating the effect of inverter dead-time, in the synchronously revolving dq reference frame. Simulation results based on this dynamic model bring out the impact of inverter dead-time on both the transient response and steady-state operation of the motor drive. For the purpose of steady-state analysis, the dynamic model of the motor drive is used to derive a steady-state model, which is found to be non-linear. The steady-state model shows that the impact of dead-time can be seen as an additional resistance in the stator circuit, whose value depends on the stator current. Towards precise evaluation of this dead-time equivalent resistance, an analytical expression is proposed for the same in terms of inverter dead-time, switching frequency, modulation index and load impedance. The notion of dead-time equivalent resistance is shown to simplify the solution of the non-linear steady-state model. The analytically evaluated steady-state solutions are validated through numerical simulations and experiments.     

A generalised instantaneous non-active power theory for STATCOM

A generalised instantaneous non-active power theory is presented. Comprehensive definitions of instantaneous active and non-active currents, as well as instantaneous, average and apparent powers, are proposed. These definitions have flexible forms that are applicable to different power systems, such as single-phase or multi-phase, periodic or non-periodic and balanced or unbalanced systems. By changing the averaging interval and the reference voltage, various non-active power theories can be derived from this theory. The definitions of instantaneous active and non- active currents provide an algorithm for a STATCOM to calculate the non-active current in the load current. The theory is implemented by the STATCOM, and four cases (three-phase balanced RL load, three-phase unbalanced RL load, diode rectifier load and single-phase load) are tested. The experimental results show that the STATCOM can perform instantaneous non-active power compensation, and both the fundamental non-active component and the harmonics are eliminated from the utility so that nearly unity power factor can be achieved. The STATCOM also has a fast dynamic response for transients.