层叠式悬浮电容逆变器的新型PWM控制方法

采用多电平结构是逆变器实现高电压大容量化的有效途径。层叠式悬浮电容多电平结构可以大大减小电容器的尺寸,并且还具有控制灵活、电平数易扩展等诸多优点,因而倍受青睐,但是该逆变器也存在悬浮电容电压的平衡控制问题。据此本文提出一种新型的PWM方法,该方法不但能够有效控制电容电压的平衡,而且算法计算量小、便于数字化实现,能够保证功率器件的开关频率均衡,利用层叠式五电平逆变器,对该方法的有效性进行了详尽的仿真验证。     

有效电容可调的单相电容电动机

为了使单相电容电动机具有良好的起动性能和运行性能,与副绕组串联的电容器需要不同的电容量.现在最普遍的作法是配置二只电容器,一只用于改善起动性能, 另一只用于改善运行性能.木文阐述应用电子开关周期性短接电容器,以获得可调的有效电容,从而达到上述目的的原理及方法.该法只需用一只电容器即可同时改善起动和运行性能.在250W 4极电容电动机上试验结果,与应用二只电容器的方法相比较,具有相近的起动性能.     

A novel quasi‐Z‐source indirect matrix converter

A new type of three‐phase quasi‐Z‐source indirect matrix converter (QZS‐IMC) is proposed in this paper. It uses a unique impedance network for achieving voltage‐boost capability and making the input current in continuous conduction mode (CCM) to eliminate the input filter. The complete modulation strategy is proposed to operate the QZS‐IMC. Meanwhile, a closed‐loop DC‐link peak voltage control strategy is proposed, and the DC‐link peak voltage is estimated by measuring both the input and capacitor voltages. With this proposed technique, a high‐performance output voltage control can be achieved with an excellent transient performance even if there are input voltage and load current variations. The controller is designed by using the small‐signal model. Vector control scheme of the induction motor is combined with the QZS‐IMC to achieve the motor drive. A QZS‐IMC prototype is built in laboratory, and experimental results verify the operating principle and theoretical analysis of the proposed converter. The simulation tests of QZS‐IMC based inductor motor drive are carried out to validate the proposed converter's application in motor drive. Copyright © 2013 John Wiley & Sons, Ltd.     

Voltage and Cable Impedance Unbalance in Submergible Oil Well Pumps

Induction motors used with submergible oil well pumps are operated in harsh environments with extreme temperatures, and any additional motor heating caused by unbalanced currents must be minimized to extend insulation life. Since the pump is usually more than a mile deep, motor voltages may be'substantially different from the voltages measured at the surface, a situation further aggravated by the use of flat cable. The results presented correlate measured and calculated values of current and relate current unbalance to unbalances in surface voltages and cable impedances. Generally, cable insulation leakage and capacitance are sufficiently negligible that motor currents are virtually the same as currents measured at the surface; however, with excessive leakage or transformer connections permitting the cable armor to be used as a ground return, this may not be true, and attempts at surface current balancing could actually increase motor current unbalance. Finally, a method for flat cable compensation is presented which appears to minimize cable impedance effects for a fixed amount of voltage unbalance.     

半桥变换器与多变压器次级串联的超级电容均压

针对于超级电容串联储能系统中单体电压不均衡的问题,介绍了一种基于半桥变换器和多变压器次级串联的均压电路,可利用多次级绕组减小因变压器单元漏感误差而引起的超级电容单体电压不均衡。该电路结构简单,还可以均衡超级电容器的电压,恒定开关频率和占空比时不需要反馈控制环节。通过分析半桥变换器每个工作模态,建立了输出电压方程,推导了串联超级电容电压均衡方程。根据电路特性,分析了变压器匝比设计方程及实现软开关变压器原边漏感要求。仿真及实验结果表明此均压电路具有均压速度快且均压效果好的特点。     

On-line search based pulsating torque compensation of a fault modesingle-phase variable frequency induction motor drive

Improved reliability and fault tolerant operation of inverter-fed variable frequency AC motor drives are very important for critical industrial applications. The paper describes variable frequency, variable voltage operation of a three-phase induction motor drive in single-phase mode for inverter fault conditions, such as open base drive and device short circuit. The detailed mathematical analysis of the machine in single-phase mode indicates that odd harmonic voltages of appropriate magnitude and phase can be injected at the machine terminal to neutralize the large low-frequency pulsating torques so as to permit smooth drive operation. The magnitude and phase angle of the desired harmonic voltages have been derived theoretically. However, to eliminate the parameter variation effect and operating point dependencies, a general purpose search algorithm has been proposed in the paper which fabricates the desired harmonic voltages on a real time basis. The search algorithm was initially exercised manually on a simulated drive system to prove its validity, and than tested extensively on a volts/hertz controlled 3-hp drive system in the laboratory     

三电平直流变换器的交错式PWM方法

三电平结构可将开关管的电压应力箝位于输入电压的一半,因此在高输入电压场合得到了广泛应用。为保证三电平变换器的正常运行,输入分压电容和隔直电容上的电压必须基本平衡,而实际电路中驱动电路延时不一致等问题可能导致电压失衡。本文提出了一种具有更强均压能力的脉冲宽度调制PWM(pulse width modulation)方法 ,该方法通过交错使用两种传统的PWM方法实现。交错式PWM方法将隔直电容电压与输入分压电容电压解耦,同时保证前者一直维持在理想值附近,大大简化了采样电路和均压策略,因此只需要调节驱动信号间的相位差便可以实现电压平衡。实验结果验证了所提调制方法和均压策略的有效性。     

A Method of Voltage Unbalance Compensation in a Y‐Connected Modular Multilevel Converter

A STATCOM is expected to be suitable for use as voltage control equipment for a distribution system that needs to be controlled to suppress the voltage deviation caused by an increase in the number of photovoltaic energy sources. A Y‐connected MMC is a promising alternative for the STATCOM circuit topology. However, it is known that the Y‐connected MMC cannot achieve capacitor voltage balance between phases with unbalance current output in order to compensate system voltage unbalance. To solve this problem, we propose a novel method to control the capacitor voltage for unbalance current output. The proposed control involves feedforward and feedback zero sequence voltage control. The feedforward control prevents capacitor voltage unbalance between phases, which is caused by the unbalance current that the Y‐connected MMC outputs. The feedback control cancels the remaining control error of the feedforward control. We verified the performance of this control through transient simulation. The Y‐connected MMC with the proposed control can realize capacitor voltage balance between phases even when the Y‐connected MMC outputs an unbalance current. Additionally, we determined the maximum unbalance current output produced by the Y‐connected MMC in relation to the rated capacitor voltage.     

偏置电容法电网电容电流测量分析

中压电网的系统电容电流是一个非常重要的参数,消弧线圈的安装、铁磁谐振的研究以及分析电压互感器高压侧保险熔断原因等都需要这个参数.文章介绍了中压电网电容电流间接测量方法(偏置电容法)的原理;详细分析了偏置电容法产生测量误差的原因,并给出了测量结果相对误差值与三相电压不平衡度以及偏置电容取值关系的定量表达式,同时指出了现场应用时为减小误差需注意的方面;误差分析表明,偏置电容法在三相电压不平衡度较小时可以满足测量精度的要求.     

基于粒子群优化算法的孤岛微电网电压不平衡补偿协调控制

微电网系统孤岛运行条件下,其系统电压完全由网内众微电网逆变器协调运行提供支撑,微电网逆变器控制性能将决定网内供电电压质量的优劣。考虑到微电网中大量单相负荷的存在,系统负荷实则通常表征为不平衡,容易引起系统电压的不平衡。针对这一问题,以同时兼顾微电网逆变器端口电压及公共连接点(PCC)电压不平衡度控制为目标,从分析电压不平衡机理入手,提出一种基于粒子群优化算法的负序电压补偿算法。补偿算法以逆变器端口电压和PCC电压不平衡度作为约束条件建立目标函数,同时考虑逆变器间的环流问题,在实现逆变器端口及PCC电压不平衡控制的同时减小逆变器间的环流。最后,分别基于MATLAB及某电力电子实时仿真平台搭建了系统仿真模型和半实物实时仿真模型,仿真及实验结果验证了所提方法的正确性和有效性。     

平板电极型激光触发真空开关的导通特性研究

强激光触发方式的真空开关由于触发精度高、可靠性好、并能有效避免触发装置的电磁干扰,在快速关合开关、电磁发射、串联补偿电容保护等领域具有非常广阔的应用前景。设计了一种平板电极型激光触发真空开关。为了提高其触发寿命,针对触发电极进行优化。触发电极耐烧蚀,靶材选取TiH_2,其能为开关导通提供丰富的初始等离子体,开关的触发性能得到加强,开关的最短时延可达650 ns。详细讨论激光参数、聚焦镜位置、主电压值等对开关的触发阈值、最低工作电压和时延特性的影响,提出触发阈值理论和电弧形成机制,为此类开关的性能优化提供理论依据。实验表明:开关稳定的触发阈值达4.5×10~7W/cm~2,最低工作电压为30 V;采用正常聚焦模式能大幅度降低开关的时延;电弧电流的开始阶段存在强烈振荡过程,电流值大于5 A后,如果外加电压足够高,振荡现象消失,真空电弧稳定燃烧。     

Causes and effects of unbalanced voltages serving an inductionmotor

A common requirement of a distribution system is to serve a combination of single-phase lighting loads and a three-phase induction motor. Two transformer connections for providing this combination service are the ungrounded wye-delta and the open wye-open delta. Each connection has its good points and bad points. Of concern are the three-phase voltages provided the induction motor. If the voltages are unbalanced, depending upon the degree of unbalance, the induction motor is subject to overheating. Sources of the voltage unbalance can be the unequal spacing between conductors of the primary and secondary lines, the transformer ratings and connection, and the amount of single-phase load relative to the three-phase load. This paper utilizes previously published models of the primary and secondary lines, transformer connections, and induction motors. A simple system is developed to demonstrate the voltage unbalance created by these components under normal and abnormal conditions and the effect of the resulting unbalances on the induction motor. The system model also provides an insight into the voltages that can appear across the transformer terminals during abnormal operating conditions     

An active line conditioner to balance voltages in a three-phasesystem

In this paper a new configuration for an active line conditioner is proposed to correct dynamically voltage unbalances in a three-phase AC system. In the proposed system it is shown that the injection of a correction voltage V_inj in one phase is sufficient to nullify the negative sequence voltage component in the incoming three phase supply. The resulting three phase voltages at the load terminals are essentially positive sequence voltages and hence are balanced. It is further shown that the kVA requirement of the proposed active line conditioner is small, typically 3% for a ten percentage unbalance in the input supply. The dynamic cancellation of the negative sequence voltage component by the proposed scheme drastically improves the performance of induction motor loads connected to a weak AC system. A thorough analysis of the scheme along with the suitable design guides are presented. Finally selected experimental results on a laboratory prototype active line conditioner are detailed     

基于有源箝位的功率器件串联均压技术

功率器件串联的关键技术挑战是如何实现串联器件的动、静态均压。提出一种基于有源箝位的器件串联均压电路及其控制方法。所述均压电路仅由1个辅助开关管和1个箝位电容串联而成,该电路与各主功率管并联。主功率管的关断电压可自动被箝位电容电压箝位,从而将器件串联均压问题转化为各箝位电容电压均衡问题。提出了一种箝位电容均压方法,利用负向电流回收箝位电容电能,并能保证辅助开关管实现零电压开通。所提均压技术具有结构简单、损耗低、模块化等优点。此外,通过调整箝位电容放电时间差异,形成阶梯型桥臂电压,以减小桥臂电压的瞬时变化率dv/dt。搭建一台 3 kV/750 V 30 kW 谐振型直流变压器样机,每个桥臂采用6个SiC MOSFET串联。实验结果表明所提均压方法在各个工况下均能实现串联器件的动、静态均压,不均压度小于3 %,且在3 kV输入电压下峰值效率达98.4 %。     

配电台区电能质量问题的混合补偿的研究

针对配电台区普遍存在的无功不足和三相不平衡的问题,本文分析了无功功率和三相不平衡调节的原理。结合现有的纯动态补偿装置以及电容器补偿在配电台区应用的优缺点,本文以动态补偿设备运行容量最小为优化目标,提出了采用相间补偿电容、分相补偿电容与动态补偿的混合补偿方案和优化控制策略。通过混合补偿等值网络模型的建立和分析,获得了混合补偿的相关规律和容量配置方法。结合仿真模型验证了该混合补偿的优化控制策略可实现纯动态补偿的一致的补偿效果,同时整机损耗降低2/3的经济运行特性。最后工程应用验证了混合补偿装置配置方法的正确性和优化控制策略的可行性。     

Indirect sensing for rotor flux position of permanent magnet ACmotors operating over a wide speed range

This paper describes an indirect sensing, or sensorless, method for rotor flux position for brushless permanent magnet (BPM) motors operating over a wide speed range, while keeping maximum torque per ampere and/or maximum efficiency capabilities. The method described is particularly applicable to trapezoidal back emf type of BPM motors. The typical trapezoidal waveform of the motor internal voltages (or back emf) contains a fundamental and higher order frequency harmonics. In particular, the third harmonic component is extracted from the stator phase voltages while the fundamental and other polyphase components are eliminated via a simple summation of the three phase voltages. The resulting third harmonic signal keeps a constant phase relationship with the rotor flux for any motor speed and load condition, and is practically free of noise that can be introduced by the inverter switching, making this a robust sensing method. In contrast with indirect sensing methods based on detection of the back-emf signal that require heavy filtering, the third harmonic signal needs only a small amount of filtering to eliminate the switching frequency and its side bands. As a result, the method described here is not sensitive to filtering delays, allowing the motor to achieve a good performance over a wide speed range. Motor starting is also superior with this method since the third harmonic signal can be detected and processed at lower speeds than for the conventional method of back-emf sensing     

Phase frame analysis of the effects of voltage unbalance oninduction machines

Operating a three-phase induction motor with unbalanced voltages can lead to excessive heating. The traditional method of analyzing the operating conditions of the motor when unbalanced voltages have been applied has been to use the theory of symmetrical components. The purpose of this paper is to develop a method of analyzing the motor in the “phase frame”. The method is then applied to a typical motor to demonstrate the results of operating a motor with unbalanced voltages and the reason why a motor must be derated under these conditions     

A single phase induction motor drive with improved performance

This paper presents a new method to improve the efficiency and torque characteristics of a single phase induction motor. First, the mathematical model of the motor is analyzed. Next, a method which uses power electronic technology to improve the efficiency and starting torque of the motor is proposed. The starting capacitor and the centrifugal switch can be eliminated here. Only a running capacitor is used. A prototype system which consists of some simple hardware circuits and a TMS320C40 digital signal processor system has been implemented. Several experimental results can validate the simulated waveforms. This paper proposes a new direction in improving the performance of the single phase induction motor system.     

A Quantitative Analysis of Induction Motor Performance Improvement by SCR Voltage Control

Minimum input power and maximum efficiency operation occur at characteristic slip values which can be realized for any induction motor operating at part load by properly adjusting the amplitude of the applied stator terminal voltages. These two criteria are shown to yield perceptibly different results when the motor is driven from a silicon-controlled rectifier (SCR) voltage controller. In addition, it is demonstrated that a constant power factor controller results in an operating regime which is substantially poorer than operation at either minimum input power or maximum efficiency. It is further shown that minimum stator current and minimum power factor angle criteria yield results which are closer to the ideal than the constant power factor controller.     

交流滤波器C1电容器保护配合策略研究

以南方电网各工程采用的交流滤波器C1电容器保护配合策略及运行情况为研究对象,对三种不平衡保护原理的优劣进行分析,指出当前计数法不平衡保护原理中存在的动作灵敏性、准确性的缺陷。综合比值法、桥差法和脉冲法的原理,提出了改进脉冲不平衡保护计数定值的建议,并首次提出了多段位计数的方法。基于一些特殊运行情况,提出了与桥差保护的配合思路。