多端柔性直流输电系统新型直流电压控制策略

随着电压源型换流器的发展,多端柔性直流输电技术受到了越来越多的关注。提出一种适用于多端柔性直流输电系统的新型直流电压控制策略。该策略通过在直流电压斜率控制中引入一个公共直流参考电压,作为多点直流电压控制换流站的电压反馈控制信号。最后,在PSCAD/EMTDC中建立基于模块化多电平换流器的4端柔性直流输电仿真模型,对所提出直流电压控制策略的特性进行稳态和暂态仿真验证。仿真结果表明：利用所提出的直流电压控制策略,多端柔性直流输电系统能够稳定、可靠地运行。     

含恒功率负荷直流微电网的状态反馈电压振荡控制技术

扰动发生后新能源发电和恒功率负荷侧换流器在现有功率控制模式下所表现出的负阻抗特性,会大幅增加直流电压振荡失稳的风险.为此,首先针对直流电压振荡失稳的问题,推导含恒功率负荷两端直流微电网的小扰动线性化状态方程.其次,结合各状态变量的参与因子,选取振荡电流、电压作为可调节控制参数,将其分别引入储能换流器与恒功率负荷换流器的占空比反馈环节中,提出基于状态反馈的多端直流电压振荡控制方法.然后,利用根轨迹、Bode图分析附加状态反馈电压振荡控制技术后的直流微电网稳定裕度的变化规律,为控制参数设计提供依据.最后,搭建时域仿真系统,验证了所提出的控制方法可有效抑制直流微电网的电压振荡,显著提高系统的动态稳定性.     

全桥型DC/DC变换器的DMC-PID串级控制策略研究

研究了全桥型DC/DC变换器系统的控制方法。针对现有DC/DC变换器动态响应速度慢、抗干扰能力差的现状,提出了基于状态反馈精确线性化的动态矩阵控制-比例积分微分DMC-PID（dynamic matrix control-propor-tional integral differential）串级控制方法。应用状态空间平均法建立全桥型DC/DC变换器系统的非线性模型,通过状态反馈精确线性化后得到线性化系统。为使系统获得优良的控制性能,选取DMC-PID串级控制方法。该控制方法同时具备PID算法的鲁棒性和DMC算法的快速性和稳定性,能有效地解决电源输入电压大范围波动输出电压不能及时稳定的问题。通过仿真分析和实验验证了该方案能在各种扰动工作条件下实现对变换器输出精确、快速的控制。     

Application of a sinusoidal internal model to current control of three‐phase utility interface converters

Three‐phase voltage‐source converters are used as a utility interface. In such a case, the converter line currents are required to track sinusoidal references synchronized with the utility grid without steady‐state error. In this paper a current control method based on a sinusoidal internal model is employed. The method uses a sine transfer function with a specified resonant frequency, which is called an S compensator. The combination of a conventional PI compensator and an S compensator is called a PIS compensator. The PIS compensator ensures that the steady‐state error in response to any step changes in a reference signal at the resonant frequency and zero hertz reduces to zero. An experiment was carried out using a 1‐kVA prototype of three utility interface converters, a voltage‐source rectifier, an active power filter, and STATCOM. Almost perfect current tracking performance can be observed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(3): 54–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20064     

一种优化系统动态性能的新型SSSC控制策略

静止同步串联补偿器(SSSC)具有快速潮流控制的能力,选择好的控制策略能够充分发挥SSSC的作用。本文计及逆变器的损耗及直流侧电容电压的动态调节过程,在两相同步旋转dq坐标系下建立了SSSC的数学模型。在分析此模型的基础上提出了基于部分状态反馈的dq轴解耦策略,同时还提出了直流侧电容电压和线路有功功率的控制方法。在Matlab/Simulink动态仿真环境中搭建了SSSC的数学模型及控制系统的仿真模型,并基于该模型对直流侧电容电压调节过程、线路传输有功功率的调节过程和SSSC的暂态过程进行了仿真,仿真结果表明该控制策略的有效性和适用性。     

One‐cycle controlled quadratic buck converter

The quadratic DC‐DC converter can broaden the voltage conversion ratio, which meets the requirements of wide input voltage. However, large‐scale variation of input voltage puts forward harsh requirements on ability to resist input disturbance of control strategy. Quadratic buck converter (QBC) is pulsed nonlinear dynamic systems, so the one‐cycle control strategy based on robustness principle may provide better rejection of power source than the linear feedback control. But the traditional one‐cycle controlled QBC (TOCCQBC) suffers from poor ability against load disturbance and steady‐state error. To overcome aforementioned shortages, an improved OCCQBC is proposed by adding inductor current to diode voltage as integral variable and introducing feedback of output voltage. The paper first introduces the working principle of the QBC, and second, the OCCQBC is presented. Then, a mathematical model using small signal analysis of the OCCQBC is established, and an experimental prototype with a power of 6 W is set up. Simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the strategy.     

VSC-HVDC输电系统模式切换控制策略

分析了基于电压源换流器的高压直流(VSC-HVDC)输电系统在定直流电压控制端交流电网故障下的模式切换控制策略,提出了基于滞环和本地直流电压检测的模式切换控制,并给出了该控制的实现方法。推导了正常运行时VSC-HVDC输电系统直流功率与两侧换流器直流电压的关系式,给出了定有功功率控制端的直流电压正常工作范围的计算方法,提出了模式切换控制策略中直流电压阈值和故障穿越期间直流电压参考值的确定方法。最后,PSCAD/EMTDC仿真验证了在不同故障类型和不同运行方式下VSC-HVDC输电系统模式切换控制策略的有效性;仿真结果表明,该直流电压阈值和参考值的确定方法能够为模式切换控制策略的指令值整定与配合提供可靠参考。     

基于T型三电平变换器的SVG仿真研究

静止无功发生器(SVG)能够显著地抑制和达到实时补偿效果.对于这一优势,采取基于T型三电平变流器拓扑结构的SVG作为研究对象,通过分析获得了系统模型,是一种存在耦合项的模型;因此为了实现解耦控制,提出了一种新型的状态反馈式补偿器,使得SVG输出电流能够稳态无误差地跟踪期望信号.同时也通过相应的控制实现了直流侧电容电压的均衡与稳定.最后在仿真软件MATLAB软件中进行了验证,为三相三电平SVG的研究与发展提供了基本保障和良好的平台.     

Investigation of performance of UPFC without DC link capacitor

This paper presents an analysis of the dynamic operation of unified power flow controller without DC link capacitor. In this scheme of UPFC the shunt converter present in the static synchronous compensator is operated as a current source rectifier, which maintains a fixed DC voltage and DC current on the DC link without capacitor. The capacitor in the DC link is replaced by an AC filter on the line side with a very small value to reduce higher order harmonics. The voltage source inverter present in the series compensator is operated with space vector modulation technique. The proposed scheme is fully validated through digital simulation. The simulated results show that the DC link voltage is maintained constant without DC link capacitor; STATCOM provides good voltage regulation and static synchronous series compensator influences power flow over the transmission line. Transient responses of single machine infinite bus power system have also been presented.     

A new method of damping harmonic resonance at the DC link in a large‐capacity rectifier‐inverter system

This paper proposes a new method of damping harmonic resonance in the DC link of a large‐capacity rectifier‐inverter system, such as in rapid‐transit railways. A voltage‐source PWM converter is connected in series to the DC capacitor of the rectifier through a matching transformer, acting as a damping resistor to the DC capacitor current. No filters are needed to extract harmonic components from the DC capacitor current. This results in a quick response and highly stable damping. The relationship between the control gain of the PWM converter and the required rating is theoretically discussed. We show that the required rating is less than one‐thousandth of that previously proposed. In particular, regenerating the power consumed by the PWM converter is very important because of the large power in practical systems. Normally, an additional PWM inverter is connected to the DC bus of the PWM converter to regenerate the consumed power. The additional inverter regenerates the DC power to the AC source through a transformer. This method, however, makes the damping circuit complex, thus the proposed method for the DC‐link harmonic resonance is less practicable. In this paper, a simple and novel scheme that utilizes the DC‐link voltage of the rectifier as a DC source for the PWM converter is proposed. The excellent practicability of the proposed damping method with the novel regenerating scheme is confirmed using digital computer simulation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(2): 53–62, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10172     

Nonlinear single-loop control of the parallel converters for a fuel cell power source used in DC grid applications

This paper presents an innovative control law for a multiphase interleaved converter in the distribution of power supply in fuel cell (FC) generators. Traditionally, to control the DC output power, voltage, or current in a converter, a linear multiple-loop feedback control technique is used. The nonlinear multiple-loop feedback control approach offers several techniques that help to improve the system response. In this paper, an alternative nonlinear single-loop feedback control scheme is proposed. This scheme is based on the differential flatness concept, which provides a solution to achieve the preferred response using a less sophisticated algorithm. To validate the proposed technique, a prototype of a FC power converter (a 600-W two-phase interleaved boost DC–DC converter) was constructed in the laboratory, and the control algorithm was implemented to control the prototype using a dSPACE 1104 controller card. The control scheme exhibited excellent experimental results for use with a 1.2-kW Nexa Ballard polymer electrolyte membrane fuel cell (PEMFC) regarding the steady state and dynamic responses as well as the control robustness.     

低输入直流电压的单级双向并网变换器设计

为了实现储能系统接入电网,设计了一种可接入低直流电压的双向单级并网变换器.所提出的双向并网变换器包含了1个双向直流变换电路和1个全桥电路.双向直流变换电路具有升压和降压调节能力,可在低输入直流电压和整流后的正弦电压之间执行双向功率转换.全桥电路基于前馈标称电压补偿器和重复控制算法将整流后的正弦电能并入电网,前馈标称电压...     

DC-bus voltage control of three-phase AC/DC PWM converters usingfeedback linearization

In this paper, a fast voltage control strategy of three-phase AC/DC pulsewidth modulation (PWM) converters applying a feedback linearization technique is proposed. First, incorporating the power balance of the input and output sides in system modeling, a nonlinear model of the PWM converter is derived with state variables such as AC input currents and DC output voltage. Then, by input-output feedback linearization, the system is linearized and a state feedback control law is obtained by pole placement. With this control scheme, output voltage responses become faster than those in a conventional cascade control structure. For robust control to parameter variations, integrators are added to the exact feedback control law. Since the fast voltage control is feasible for load changes, it is shown that the DC electrolytic capacitor size can be reduced. In addition, the capacitor current is analyzed for size reduction of the capacitor. As is usual with PWM converters, the input current is regulated to be sinusoidal and the source power factor can be controlled at unity. The experimental results are provided to verify the validity of the proposed control algorithm for a 1.5 kVA insulated gate bipolar transistor PWM converter system     

Voltage balancing control of chain link converter application to interconnection system

An application of the chain link converter (CLC) system, which consists of multiple single‐phase voltage source converters (VSCs) connected in parallel or series, is studied as interconnection systems. In a CLC‐high voltage direct current transmission (HVDC) system, single‐phase converters must be connected in series on the DC side to make the DC voltage high, and the DC voltage of each converter must be controlled to the same value to get an appropriate capacity. This paper describes a DC voltage balancing control (DVBC) method between series converters. Simulations and simulator tests in steady states and in transient states were carried out to confirm behaviors of the CLC‐HVDC system. Those results confirmed the viability of CLC applications to interconnection systems. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fuzzy bilinear state feedback control design based on TS fuzzy bilinear model for DC–DC converters

This paper proposes a fuzzy bilinear state feedback controller based on Tagaki–Sugeno (TS) fuzzy bilinear model for DC–DC converters. The DC–DC converters can be approximated to bilinear model via Taylor series expansion. For achieving the output voltage regulation, we formulate the extended system of bilinear DC–DC converter model, one of whose state variables is the error between the output voltage and the reference output voltage. The extended system can be described to TS fuzzy bilinear model. We design a fuzzy bilinear state feedback controller to track the reference output voltage. The closed loop system is globally asymptotically stable via the proposed controller. Lyapunov theory is employed to guarantee the stability of the closed loop system. Numerical examples are given to demonstrate the validity of our proposed control approach with comparative results.     

VSC-HVDC系统新型广义直流电压控制策略

建立了基于电压源换流器（VSC）的高压直流（HVDC）（VSC-HVDC）输电系统的标幺值数学模型。为了抑制系统故障时直流电压的波动幅度,基于上述模型,提出了一种新型广义直流电压控制策略。在此控制策略下,换流站间不需要通信,外环有功功率控制器为一个广义直流电压控制器（GDCVC）。当直流电压因交流系统受到扰动或直流电压控制器（DCVC）故障等原因而不能有效维持直流电压时,维持和限制直流电压的功能可平滑、自动地由有功功率控制器接替,从而达到保护设备安全运行、提高系统持续运行能力的目的。仿真表明,文中提出的控制策略在稳态和暂态过程中均具有良好的控制效果,对实际VSC-HVDC系统的控制器设计具有参考意义。     

考虑直流电压无差调节的MMC-MTDC协调下垂控制策略

直流电压稳定对多端直流输电(MTDC)系统的安全可靠稳定运行至关重要,对此提出一种新型协调下垂控制策略。通过建立MTDC系统的等效网络模型,推导小信号解析式,然后将小信号补偿量注入传统下垂控制中,实现MTDC系统在不同工况下直流电压的无差调节。采用PSCAD/EMTDC建立了基于模块化多电平换流器的四端直流输电系统的仿真模型,仿真结果验证了所提控制方法的有效性。在所提控制方法作用下,直流电压在扰动下会恢复到原来的稳态运行状态,避免了传统下垂控制产生的直流电压偏差,实现了直流电压的额定值运行。     

Real and reactive power coordination for a unified power flow controller

This paper proposes a new real and reactive power coordination controller for a unified power flow controller (UPFC). The basic control for the UPFC is such that the series converter of the UPFC controls the transmission line real/reactive power flow and the shunt converter of the UPFC controls the UPFC bus voltage/shunt reactive power and the DC link capacitor voltage. In steady state, the real power demand of the series converter is supplied by the shunt converter of the UPFC. To avoid instability/loss of DC link capacitor voltage during transient conditions, a new real power coordination controller has been designed. The need for reactive power coordination controller for UPFC arises from the fact that excessive bus voltage (the bus to which the shunt converter is connected) excursions occur during reactive power transfers. A new reactive power coordination controller has been designed to limit excessive voltage excursions during reactive power transfers. PSCAD-EMTDC simulation results have been presented to show the improvement in the performance of the UPFC control with the proposed real power and reactive power coordination controller.     

基于STATCOM/ESS的光伏低压穿越控制策略

为了提高光伏并网系统的低压穿越(Low Voltage Ride Through,LVRT)能力,将储能系统(Energy Storage System,ESS)和静止同步补偿器(Static Synchronous Compensator,STATCOM)组成新型功率补偿装置STATCOM/ESS引入光伏并网发电系统。当电网侧发生电压跌落时,STATCOM/ESS不但提供的无功功率可以支撑并网点电压,同时吸收多余的有功功率避免对光伏发电系统的危害,电压恢复后将储存的能量返送回电网,高效利用能源。为便于功率双向流动,STATCOM与ESS之间采用双有源主动桥(Dual Active Bridge,DAB)直流变换器连接。针对DAB变换器,提出一种改进的双移相控制策略,来减小DAB变换器的回流功率。仿真结果表明,提出的控制策略在一定范围内将回流功率限制为零,显著提升光伏并网系统的低压穿越能力,提高光伏并网系统的稳定性,具有良好的灵活性和优越性。