A constant DC voltage control‐based strategy for an active power quality compensator in electrified railways with improved response

This paper proposes a constant DC voltage control‐based strategy for an active power quality compensator (APQC) used in electrified railways. The proposed strategy consists of only an I‐PD‐based constant DC capacitor voltage control with an added moving‐average type low‐pass filter (LPF). The added LPF improves the response of the constant DC capacitor voltage control for the APQC. Thus we offer the simplest control method for the APQC used in electrified railways with improved response. The basic principle of the proposed control strategy is discussed in detail, and then confirmed by digital computer simulation using the PSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that balanced source currents with unity power factor are obtained on the primary side of the Scott transformer in the traction substation systems, improving the response by one‐fourth as compared to that of the previously proposed control method. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A constant DC voltage control based compensation method of an active power quality compensator for electrified railways

This paper proposes a novel and simple control method for the active power quality compensators (APQCs) used in electrified railways. The proposed method uses only the constant dc capacitor voltage control block, which is commonly used in the APQCs. No detection blocks of the harmonic, reactive, and negative-sequence components are necessary. Thus we offer the simplest way to compensate the harmonic, reactive, and negative-sequence currents on the primary side of the Scott transformer in the traction substation. The basic principle of the proposed control method is discussed in detail, and then confirmed by digital computer simulation usingPSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that the balanced source currents with the unity power factor are obtained on the primary side with the proposed control method, which uses only the constant dc capacitor voltage control. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A new control method of a resonant switched‐capacitor converter and the application for balancing of the split DC voltages in a multilevel inverter

This paper proposes a new voltage‐balancing circuit for the split DC voltages in a diode‐clamped five‐level inverter. The proposed circuit is based on a resonant switched‐capacitor converter (RSCC), which consists of two half‐bridge inverters, a resonant inductor, and a resonant capacitor. A new phase‐shift control of the RSCC is proposed to improve voltage balancing performance. Theoretical analysis reveals the rating of the RSCC and stored energy in the resonant inductor. Experimental results confirm the reduction of the inductor to one‐tenth in volume compared to a conventional voltage‐balancing circuit based on buck‐boost topology. Moreover, the proposed phase‐shift control has demonstrated that it is possible to eliminate the voltage deviation between the DC capacitors. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(2): 69–79, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20719     

Voltage fluctuation compensator for Shinkansen

In AC electric railways, three‐phase voltage is changed into the single‐phase circuit of two circuits with the Scott‐connected transformer. If unbalancing of the load between single‐phase circuits becomes large, voltage fluctuation becomes large on the three‐phase side. Railway static power conditioner (RPC) was developed for the purpose of controlling voltage fluctuation on the three‐phase side. An RPC is comprised of a pair of self‐commutated PWM inverters. These inverters connect the main phase and teaser feeding buses, coupled with a DC side capacitor such as a back‐to‐back (BTB) converter. In this way, the two self‐commutated inverters can act as a static var compensator (SVC) to compensate for the reactive power and as an active power accommodator from one feeding bus to another. 20 MVA/60 kV RPCs started commercial operation in 2002 at each two substations on the newly extended Tohoku Shinkansen for compensating voltage fluctuation on the three‐phase side caused by traction loads, absorbing harmonic current. The results of operational testing indicate that an RPC can accommodate single‐phase loads such as those of PWM‐controlled Shinkansen and thyristor phase‐controlled Shinkansen, and handle the exciting rush current of transformers, as well as compensate for harmonics successfully. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(4): 25–34, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20397     

基于滑模控制的TPESFTI驱动DFIG系统FCS-MPC

针对双馈异步风力发电机(DFIG)系统中机侧PNC型三电平逆变器的某桥臂发生故障时,提出了一种三相八开关容错逆变器(TPESFTI)控制策略,并给出了其拓扑结构和输出电压模型;考虑TPESFTI中母线电压分压不均衡等问题,研究分析直流侧电容电压不平衡的原因,给出了其相应的不平衡电压动态模型,并利用有限控制集模型预测控制(FCS-MPC)中目标函数的非线性约束项来抑制母线电容分压不均衡对系统的不利影响;同时为了提高FCS-MPC策略的性能,提出了基于滑模控制的FCS-MPC策略。仿真结果表明,该方法不仅能够确保DFIG系统稳定运行,并且能对母线电容电压不平衡进行有效抑制,同时具有良好的动态性能和较强的抗负载能力,进一步验证该控制策略的可靠性和有效性。     

适合高输入电压的高频隔离逆变器

不带变压器的逆变器缺少电气隔离,安全程度较低。将高频隔离环节引入多电平逆变器,在具备输出电压质量高、开关管电压应力低等多电平逆变器优点的同时,实现高频电气隔离,提高安全程度,因此适用于较高输入电压的应用场合。对此,文中提出一种高频隔离九电平逆变拓扑,分析该拓扑的工作模态,设计多重载波调制策略,研究直流侧电容电压与母线电流间存在的关系,并据此设计出对电容电压存在相反影响的2种开关序列,给出直流侧电容电压均衡策略。最后,在Power Simulation中搭建仿真模型,并制作1 kVA的实验样机,仿真和实验结果验证了所提新型拓扑、控制方法及均压策略的正确性和可行性。     

Three-phase four-wire shunt active power filter based on the SOGI filter and Lyapunov function for DC bus control

The three-phase four-wire shunt active power filter (SAPF) was developed to suppress the harmonic currents generated by nonlinear loads, and for the compensation of unbalanced nonlinear load currents, reactive power, and the harmonic neutral current. In this work, we consider instantaneous reactive power theory (PQ theory) for reference current identification based on the following two algorithms: the classic low-pass filter (LPF) and the second-order generalized integrator (SOGI) filter. Furthermore, since an important process in SAPF control is the regulation of the DC bus voltage at the capacitor, a new controller based on the Lyapunov function is also proposed. A complete simulation of the resultant active filtering system confirms its validity, which uses the SOGI filter to extract the reference currents from the distorted line currents, compared with the traditional PQ theory based on LPF. In addition, the simulation performed also demonstrates the superiority of the proposed approach, for DC bus voltage control based on the Lyapunov function, compared with the traditional proportional-integral (PI) controller. Both novel approaches contribute towards an improvement in the overall performance of the system, which consists of a small rise and settling time, a very low or nonexistent overshoot, and the minimization of the total harmonic distortion (THD).     

电铁并联电容补偿装置差压保护整定方法的改进研究

并联电容补偿装置是我国电气化铁道提高功率因数、降低谐波影响的重要设备。结合电气化铁道实际负荷特性对并联电容补偿装置差压保护的现行整定方法进行了深入分析,得出由于负荷特性显著不同,电力系统常用的电容器差压保护的整定方法并不适用于3次谐波含量较大的电铁并联电容补偿装置;根据实际运行需要提出了两种不同的改进方法并进行了详细计算和比较,建议采用单支电容器开路故障退出造成的不平衡电压作为电铁并联电容补偿装置差压保护的整定值。     

基于改进载波移相SPWM的链式STATCOM电容电压平衡控制策略

介绍了传统载波移相SPWM及脉冲循环换位调制策略,指出了上述方法由于级联H逆变桥的电路参数及损耗差异等因素,无法真正实现链式STATCOM的电容电压平衡。笔者通过对传统载波移相SPWM调制策略进行改进,提出了一种新的链式STATCOM电容电压平衡控制策略,分析了该策略的基本原理与实现过程。通过PSCAD/EMTDC对该控制策略进行了仿真,结果说明,该策略可以很好地实现电容电压的平衡,而且对上层控制、装置的谐波特性不会产生影响。     

基于电压平衡器的固态变压器及其控制策略研究

固态变压器是交直流混合配电网的核心装置。针对低压直流配电网一般采用双极性供电的特点,提出了一种基于电压平衡器的固态变压器拓扑。所提拓扑的中间级DC/DC包括输入半桥、双有源桥和电压均衡3部分,结合其运行模式给出了各部分的控制策略。为了分析系统的大信号稳定性并加快仿真速度,给出了中间级DC/DC子模块的大信号回转器模型,并采用仿真方法验证了所提拓扑和控制策略的有效性。所提出的基于电压均衡器的固态变压器具有多个电压端口,能够与中高压电网及低压电网相连,提供自身用电或组网运行。     

新型直流侧串联型有源电力滤波器

通过对电压型谐波源补偿特性的分析,说明了传统并联型有源电力滤波器(active power filter,APF)补偿该类谐波源的不足,设计了一种新型的直流侧串联型APF。与传统的交流侧串联型APF相比,该APF串联在整流桥的直流侧,简化了电路结构,减少了有源开关的数量,用于对电压型谐波源的谐波治理有很大的技术优势。文中对直流侧串联型APF的电路拓扑和基本原理进行了分析,推导了相应的控制实现方程,给出了主电路主要参数(滤波电感和储能电容)的设计和选取标准,为系统的合理设计提供了理论依据。仿真结果验证了理论分析的正确性与可靠性。     

Improved “K” type seven-level switched capacitor inverter topology with Self-voltage balancing

This paper proposes an improved “K” type seven-level switched capacitor inverter topology. The proposed topology consists of eight active switches, one floating capacitor, and two dc-link capacitors. The floating capacitors are charged and discharged in each half-cycle to maintain the capacitor voltage with the same value of the input voltage. The floating capacitor voltage is self-balanced, and the output voltage is 1.5 times higher than the input voltage. To prove the superiority of the proposed topology, it is compared with the existing seven-level inverters in terms of maximum voltage stress on the switch and required the number of power components. The simulation and experimental validation are carried out for 1.6 kW, 50 Hz using a laboratory-based setup with a switching frequency of 5 kHz. The results are discussed highlighting the performance of the proposed topology for the dynamic load variations at different modulation indices. Both simulation results and experimental results have good agreement in terms of voltage balancing of flying capacitor.     

三调谐直流滤波器高压电容故障分析与保护

云—广特高压直流输电工程直流侧采用的三调谐滤波器只有一个处于高电位的电容器,该高压电容器承受几乎全部直流电压和大部分谐波电压降,导致容易在运行中发生电压击穿损坏。因此有必要对它的故障原因和故障特征进行深入分析和探讨。笔者讨论了直流高压电容器的内部结构和工作条件,接着分析了电容器单元故障时不平衡电流的大小和特征,并基于PSCAD/EMTDC工具建立详细的三调谐直流滤波器高压电容的模型,证明了其故障时不平衡电流大小与两桥臂电流之和成固定比例的关系,最后对高压电容器应配置的保护方式提出了建议。     

Three-phase two-leg buck-boost DC-AC inverter with differential power processor unit

Renewable energy sources (RESs) need power-electronics-based converters to deliver the acquired power to the grid. Those converters should provide voltage-bucking/boosting capabilities to accommodate various grid modes specially for three-phase distorted commonly unbalanced distribution utility networks. Several power electronic-based converters have been elaborated to fulfill this high-demand market. Single-stage converters are the most dominant in the market where the current source inverters (CSIs), impedance source inverters (ZSIs), and boost inverters are the high-end candidates. The aspects of cost, footprint, and minimal numbers of active switches, in addition to simplified controllability, build the main challenges that face the evolution of robust renewable energy-associated grid-tied converters. This paper presents a novel three-phase differential-mode buck-boost inverter based on two bidirectional buck-boost DC/DC converters and one differential power processor (DPP) unit. The proposed topology is a single-stage DC/AC converter offering bucking/boosting capability, with reduced hardware requirements. The proposed topology features a simplified control methodology in addition to reduced size and cost of the hardware setup which makes it more suitable for grid-tied renewable energy applications. The operation principles, small-signal model, and control strategy of the proposed topology are also illustrated. Simulation and experimental results are presented in details to verify the topology-enhanced performance under various operating conditions. The deducted results elucidate the viability of the proposed configuration alongside with the claimed merits.     

采用级联多电平逆变器的混合型有源电力滤波器

针对高电压、大容量有源电力滤波器所存在的投资大、技术实现较为困难等问题，提出一种采用单相全桥逆变器和三相逆变器构成的多电平混合型有源电力滤波器方案。在所提方案中，单相和三相逆变器采用不同的电力电子器件实现，不需要与逆变器级联的变压器，从而可降低装置的体积与成本。对多电平逆变器的控制策略、逆变器直流侧电容器电压选取等进行了分析，并以10kV系统为例进行了参数计算和仿真研究。仿真结果表明所提方案具有结构简单、补偿效果好及适合应用于高电压、大容量的谐波滤波场合等特点。     

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     

一种光伏发电用高增益多电平逆变器

针对传统的多电平逆变器存在有源器件数量较多、电容电压不平衡、结构复杂以及电压增益低的问题,提出一种降低器件数量且可扩展的多电平逆变器。该逆变器由开关电容单元和两个半桥组成,使用1个直流电源、3个电容、13个开关管,实现4倍电压增益和九电平交流输出电压。该逆变器通过2个半桥代替后端H桥转换输出电压极性,可以有效降低开关管总电压应力。在所提逆变器的扩展结构中,电容逐级充电的工作方式进一步提高了电压增益和输出电平数。首先,详细阐述了所提逆变器的工作模式、调制策略、电容分析、电压应力计算和电路参数设计。然后,与其他类似多电平逆变器进行了比较。最后,通过仿真与实验验证了所提逆变器的可行性和理论分析的正确性。     

改善微网电能质量的有源电能质量调节器研究

提出在微网交流母线和低压配网公共连接点之间并入有源电能质量调节器,可改善微网电能质量,减小微网接入对低压配网电能质量的影响.提出了基于瞬时无功理论的同步锁相方法,准确分解出公共连接点电压基波正序分量,进而求得其相位.由补偿电流控制策略计算得到参考电流,控制有源电能质量调节器实时向微网补偿谐波电流和无功电流,即使在三相负载不平衡时,使公共连接点三相电流平衡且为正弦波,从而平衡公共耦合点的三相电压.Matlab/Simulink 仿真结果证明了所提同步锁相方法和补偿电流控制策略的有效性     

模块化多电平换流器子模块拓扑设计及其控制

根据直流故障电流切断位置不同,首先分析基于交流断路器、直流断路器和模块化多电平换流器子模块拓扑的3种故障抑制技术方案及其特点。然后从切断故障电流角度出发,利用双向可控开关对半桥拓扑进行改进设计以抑制直流故障,并与传统半桥子模块相结合构成混合双子模块拓扑以降低单位电平成本和运行损耗。同时研究在闭锁期间混合双子模块内部电容不均衡充电所导致的电容电压不平衡问题及其应对策略。最后在PSCAD/EMTDC中搭建两端仿真模型,对混合双子模块拓扑直流故障抑制特性及电容电压控制策略进行仿真验证。     

一种改进的ZVZCS全桥PWM变换器

针对当前零电压、零电流全桥DC/DC变换器需要在辅助电路中增加有源或有损器件及二次侧整流二极管电压应力增大的问题,提出一种改进的电路拓扑结构并对工作过程进行了分析。电路超前臂零电压工作的实现方法与其他传统电路相同,采用外加辅助电容实现;滞后臂的零电流工作条件由2个二极管和1个电容构成的辅助电路实现。辅助电路中不含有源、有损器件,不会增加电路的额外损耗,相比其他拓扑结构,具有更高效率。由于与变压器二次侧抽头并联的钳位电容数值较大,将变压器副边的电压钳位,所以不会增加二次侧的整流管的电压应力。仿真结果验证了电路分析的正确性和设计的可行性。