A voltage-source PWM rectifier-inverter with feedforward control of instantaneous power

In general, diode rectifiers with electrolytic capacitors on the dc side have been used as dc power supplies for voltage-source inverters. Rectifiers of this type, however, cause many problems such as poor power factor and harmonics. Recently, voltage-source PWM rectifier-inverters have been studied to provide the following advantages: (1) harmonic-free on both ac sides; (2) unity power factor on the input ac side; (3) power flow of either direction or power regeneration; (4) reduction of the dc capacitor. However, it is difficult for a conventional voltage-source PWM rectifier-inverter to regulate the capacitor voltage on transient states because it has only a voltage feedback loop. This paper describes a voltage-source PWM rectifier-inverter with feedforward control of instantaneous power. Based on the pq theory, the instantaneous power which is calculated in the control circuit of the inverter is fed forward to the control circuit of the rectifier. The feedforward control of instantaneous power contributes greatly to sufficiently suppress voltage fluctuation of the dc capacitor on transient states. Transient characteristics are discussed, and some interesting experimental results of a laboratory model are shown.     

Analysis and improved control method of resonant DC link inverters

High performance power conversion requires high switching frequency power converters. Resonant dc link inverters, which are investigated in this paper, are suitable for this purpose because they cause no switching loss in principle. But in these inverters, loss of the resonant oscillation and occurrence of high peaks in the resonant capacitor voltage are serious problems. In this paper, we investigate a control method for resonant dc link inverters which can overcome these problems. First of all, we summarize the basic control principle of an ideal resonant dc link inverter. Then we present an analyzing method for the practical resonant dc link inverter introducing two equivalent circuits in which the influence of the power losses in the resonant link and in the inverter load is considered. From these equivalent circuits, the problems of existing control methods are clarified. Based on the results of this analysis, we propose an optimum and keep the capacitor voltage at an allowable level. A simple compensation method for the influence of storage time of switching devices, which affects the implementation of the proposed control method, is described. Some experimental results are included to confirm the validity of the analytical results and the effectiveness of the proposed control method.     

A voltage source PWM rectifier-inverter with feedforward control of instantaneous power

In general, diode rectifiers with electrolytic capacitors on the dc side have been used as dc power supplies for voltage source inverters. This type of rectifiers, however, causes many problems such as poor power factor and harmonics. Recently, voltage source PWM rectifier-inverters have been studied to provide the following advantages; (1) harmonic-free on both ac sides; (2) unity power factor on the input ac side; (3) power flow of either direction or power regeneration; (4) reduction of the dc capacitor. It is, however, difficult for a conventional one to regulate the capacitor voltage on transient states because of having only a voltage feed-back loop. This paper describes a voltage source PWM rectifier-inverter with feed-forward control of instantaneous power. Based on the pq theory, the instantaneous power which is calculated in the control circuit of the inverter is fed forward to the control circuit of the rectifier. The feed-forward control of instantaneous power makes a great contribution to sufficiently suppress voltage fluctuation of the dc capacitor on transient states. Transient characteristics are discussed and some interesting experimental results of a laboratory model are shown.     

一种电压源型有源电力滤波器的新型控制方法

研究了电压源型有源电力滤波器、电源及非线性负载三者之间的能量交换机理,分析了变流器直流侧电容电压的稳定问题,提出了维持直流侧电容电压稳定的新方法。在此基础上提出了一种电压源型有源电力滤波器的新型控制方法,详细推导了控制方程。该方法无需检测三相负载电流和三相输入电压,无需计算参考电流、无功电流和谐波电流;只需检测两相电源电流和直流侧电容电压,通过简单运算就可直接求出每个开关周期内各开关的占空比,实现滤波器的控制。仿真研究结果表明新型控制方法能有效补偿谐波电流和无功电流,抑制负载不对称。     

Elimination of low-frequency harmonics caused by PWM in athree-phase soft-switched boost rectifier

This paper presents three major causes of low-frequency harmonics in a high-frequency soft-switched three-phase pulsewidth modulation (PWM) boost rectifier: pulsewidth limits; an improper space-vector modulation scheme; and dead time. Among these, the pulsewidth limits are related to soft-switching techniques. To eliminate undesirable low-frequency harmonics, each cause is illustrated and a solution is provided. Both simulation and experimental results prove the effectiveness of the proposed solutions. Due to the similarities between boost rectifiers and voltage-source inverters, the conclusions of this paper are also applicable to high-frequency PWM voltage-source inverters     

Multilevel DC-link inverter

This paper presents a new class of multilevel inverters based on a multilevel dc link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes, or capacitors. An MLDCL can be a diode-clamped phase leg, a flying-capacitor phase leg, or cascaded half-bridge cells with each cell having its own dc source. A multilevel voltage-source inverter can be formed by connecting one of the MLDCLs with a single-phase bridge inverter. The MLDCL provides a dc voltage with the shape of a staircase approximating the rectified shape of a commanded sinusoidal wave, with or without pulsewidth modulation, to the bridge inverter, which in turn alternates the polarity to produce an ac voltage. Compared with the cascaded H-bridge, diode-clamped, and flying-capacitor multilevel inverters, the MLDCL inverters can significantly reduce the switch count as well as the number of gate drivers as the number of voltage levels increases. For a given number of voltage levels m, the required number of active switches is 2/spl times/(m-1) for the existing multilevel inverters but is m+3 for the MLDCL inverters. Simulation and experimental results are included to verify the operating principles of the MLDCL inverters.     

DC–AC Cascaded H-Bridge Multilevel Boost Inverter With No Inductors for Electric/Hybrid Electric Vehicle Applications

This paper presents a cascaded H-bridge multilevel boost inverter for electric vehicle (EV) and hybrid EV (HEV) applications implemented without the use of inductors. Currently available power inverter systems for HEVs use a dc–dc boost converter to boost the battery voltage for a traditional three-phase inverter. The present HEV traction drive inverters have low power density, are expensive, and have low efficiency because they need a bulky inductor. A cascaded H-bridge multilevel boost inverter design for EV and HEV applications implemented without the use of inductors is proposed in this paper. Traditionally, each H-bridge needs a dc power supply. The proposed design uses a standard three-leg inverter (one leg for each phase) and an H-bridge in series with each inverter leg which uses a capacitor as the dc power source. A fundamental switching scheme is used to do modulation control and to produce a five-level phase voltage. Experiments show that the proposed dc–ac cascaded H-bridge multilevel boost inverter can output a boosted ac voltage without the use of inductors.      

高压电容器充电电源的研究

为了研究电容器放电结束后的能量补充,推进电容器充电电源(CCPS)根据电容器输出电压的要求,对带电阻器的高压直流电源、谐振充电电源和高频变换器充电电源技术进行了讨论,并对其进行了验证和对比。带电阻器的高压直流电源电路简单,但是体积庞大,效率低下,适用于要求不高的场合;谐振充电电源对开关的耐压和电容容量要求很高,调整率很差;高频变换器采用电力电子和现代控制技术,使得充电电源运行起来更安全、可靠、易控,是目前采用的主要技术。另外,因三相谐振充电电源和并联模块充电电源是大功率充电电源的发展方向,故应根据需要选择充电方式和电路结构,以达到更高的性价比。     

三相光伏并网逆变器电网高阻抗谐振抑制方法

针对电网电压高阻抗LCL滤波器谐振问题,提出一种虚拟电阻+电容有源阻尼方法。该方法将虚拟电阻和电容串联之后与三相光伏并网逆变器的滤波电容并联。通过滤波电容电压得到虚拟电阻和电容支路的电流,将虚拟电阻和电容支路的电流作为LCL滤波器谐振抑制有源阻尼电流给定。通过逆变侧电流闭环控制,实现对三相光伏并网逆变器电网高阻抗LCL滤波器谐振抑制。建立15 k W的T型三电平三相光伏逆变器平台,对所提有源阻尼方法进行稳态实验,实验结果验证所提方法的可行性和正确性。     

HVDC transmission system using multilevel power converters based on dual three-phase two-level inverters

Multilevel converters are now an attractive solution for high-voltage direct-current (HVDC) electrical energy transmission systems. Unlike the well-known two-level voltage source converters, multilevel converters use 3 or more voltage levels or steps per leg to modulate the ac voltages, decreasing voltage distortion and reducing electromagnetic interference. This work presents a HVDC transmission system based on a new multilevel structure using a dual two-level converter topology. This structure attains multilevel operation and advantages using two well known three-phase voltage source two-level inverters connected to one three-phase open windings transformer. The proposed dual converter structure has two independent dc links allowing each inverter to process half of the total power. This arrangement is fitted with a control system designed to control the active and reactive power towards their specific set point values, while balancing the voltages of the two dc link capacitors in real time. Obtained results show the effectiveness of the proposed HVDC transmission system.     

400Hz中频单相电压源逆变器的并联运行控制

针对两个并联联接的单相电压源逆变器进行了详细的电路分析,证明了每个逆变器输出电压的幅值和相位可以分别由其输出功率的无功分量和有功分量单独控制。并针对400Hz逆变器的特点。提出了一种共享同步信号的外特性下垂控制方法,取得了很好的均流效果。通过在Matlab上的仿真和在两台1．5kW样机上的实验．证明了该方案的有效性。     

New control approach for capacitor supported DSTATCOM in three-phase four wire distribution system under non-ideal supply voltage conditions based on synchronous reference frame theory

A large number of single-phase linear and non-linear loads may be supplied from three phase ac mains with neutral conductor. They cause excessive neutral current, harmonics and reactive power burden and unbalance. A four wire DSTATCOM (distribution static compensator) is used for neutral current compensation along with reactive power compensation, harmonics elimination and load balancing. A novel control approach is proposed for the control of four wire DSTATCOM under non-ideal supply voltage conditions. A four-leg voltage-source converter (VSC) with a dc capacitor is used as a four wire DSTATCOM. The proposed control approach is based on synchronous reference frame (SRF) theory and an indirect current control technique. The switching signals for the voltage-source converter (VSC) of the DSTATCOM are derived from the estimated reference supply currents. The load balancing, harmonics elimination and the neutral current compensation are demonstrated along with unity power factor (UPF) and zero voltage regulation (ZVR) modes of operation. Simulation results based on MATLAB software with its Simulink and power system blockset (PSB) toolboxes are presented to validate the control strategy. The DSTATCOM is able to maintain the self-supported dc bus under various disturbances.     

双向连续可调无功的SPWM型静止无功补偿器

提出了一种双向连续可调无功的主电路拓扑。该补偿器结合正弦脉宽调制（SPWM）型逆变器直接调节补偿电容器和电抗器上的电压,实现补偿器双向连续可调无功,非常适合于中低压配电系统的无功补偿;克服了传统晶闸管控制电抗器的谐波问题;此外,逆变器的工作容量仅为补偿容量的25%。主电路拓扑采用三相四桥臂结构,可以采用分相控制对负荷无功、不对称等问题进行有效的补偿。最后通过实验验证了该补偿器的可行性和有效性。     

基于三相供电电压偏差选取直流电容参数研究

在电压型PWM AC/DC/AC变换中,直流侧储能滤波电容参数的选取是变换器稳定运行的关键因素之一。针对目前直流侧电容选取存在一定的不精确性,分析了AC/DC/AC变换电路稳态时直流电容充放电的原理,对变换器交直流侧电压的关系进行研究,建立了电容纹波电压与三相供电电压偏差之间的数学模型,提出了基于三相供电电压偏差选取直流侧电容参数的方法。分别对单相和三相不可控整流电路提供直流电源时直流侧电容C的合理选取给出了相应的分析和计算,并通过仿真和试验验证了直流储能滤波电容参数确定方法的有效性。     

混合四电平电压源逆变器及其中点电位控制

针对传统多电平逆变器结构较复杂的缺点,提出了一种混合四电平三相三桥臂电压源逆变器的拓扑结构及其中点电位控制方法,该拓扑结构将直流侧三个分压电容的电压调整为1∶2∶1的比例,利用相与相之间的电压差来实现与传统五电平结构相同的输出线电压电平数。与传统NPC型五电平逆变器相比,该结构所需开关器件更少,具有更高的经济效益。针对拓扑结构提出的中点电位控制方法,能够实现直流侧电容电压的平衡。通过在给定条件下的MATLAB/Simulink仿真验证,仿真结果为中频逆变电源的开发研制提供了一定的参考依据。     

A vector control system using a neutral-point-clamped voltage-source pwm inverter

This paper describes a vector control system of an induction machine using a neutral-point-clamped voltage-source inverter (NPC-VSI) that is one of the double series-connected inverters. The NPC-VSI is able to output five-level step-shaped line-to-line voltage without output transformers or reactors, and it may reduce harmonic currents corresponding to torque ripples. However, the NPC-VSI has a problem in that excessive high voltage is applied to switching devices when a neutral point of two dc capacitors of the NPC-VSI varies from the center of the dc link voltage, because the neutral point is floating. This paper proposes also a current controller to which the space vector theory is applied. This can reduce harmonic currents to one-fourth those of a conventional voltage-source inverter using six switching devices, and regulate the neutral point potential within a preset range. To simplify the current controller, information about voltage space vectors is given from the vector controller to the current controller. The validity of the current controller is confirmed by a prototype using an induction machine of 2.2 kW.     

采用数字控制的400 Hz大功率逆变电源

详细分析数字控制对400 Hz大功率逆变电源特性尤其是计算延时对电感电流反馈环或电容电流反馈环带宽的影响。分析表明数字控制使得电流反馈环带宽大大减小,逆变电源无法抑制由于死区时间以及非线性负载等非线性因素产生的低次谐波,降低了电源的性能。分析其它采用电压、电流双闭环数字控制的400 Hz逆变电源必须采用幅值环作为外环控制的原因,并指出其存在的缺点。为了获得高性能的控制效果,提出一种基于谐振控制器的新型的单电压环控制策略,并分析现有文献中谐振控制器的不同离散化方法之间的关系,进而提出谐振控制器数字化实现的一种更为直接的方法。所提出的数字化控制方法简单易行,可以实现特定谐波的完全消除,即便在定点数字信号处理器(digital signal processor,DSP)上也能很好地实现。在16位定点DSP控制的三相90 kVA组合式400 Hz逆变电源上的线性负载以及非线性负载实验表明,该方法正确可行,性能优良。     

400Hz中频单相电压源逆变器的输出控制及其并联运行控制

中频电源由于其较高的输出频率，要想得到较好的输出电压波形和较大的输出功率，则比工频逆变器的控制更加困难。针对400Hz中频逆变器的特点，给出了一种带幅值环的双闭环单相逆变器控制策略，得到了很好输出波形。并提出了一种介于有线和无线并联控制方法之间的共享同步信号的外特性下垂控制方法，以及用于消除直流环流的直流偏置电压下垂方法，将上述方法应用于中频逆变电源的并联运行控制，取得了很好的均流效果。介绍了该方案的理论依据，并搭建了两台1.5kW的实验样机，实验结果证明了该方案的有效性。     

PWM-VSI inverter-assisted stand-alone dual stator winding induction generator

This paper presents a novel usage of a dual stator winding three-phase induction machine as a stand-alone generator with both controlled output load voltage magnitude and frequency. This generator, with both three-phase power and control windings housed in the stator structure, has the load connected to the power winding and a three-phase pulsewidth modulation (PWM) voltage-source inverter sourcing the control winding. The input to the PWM inverter is either a battery source or a charged DC capacitor. The operational characteristics of these generator schemes with either of the two inverter sources are investigated and shown to have desirable performance. How the load voltage magnitude depends on the various control and design parameters such as rotor speed, compensating capacitance, and load impedance is determined using a detailed mathematical model of the system.     

一种单相MMC预充电控制策略

模块化多电平换流器(MMC)的预充电通常可分为两个阶段:不控整流以及boost升压。三相MMC的boost升压控制技术已经较为成熟。然而与三相MMC不同的是,单相MMC的直流侧具有独立电容。因此,单相MMC的boost升压阶段必须同时考虑子模块电容和直流侧电容,这是单相MMC预充电的难点所在。文中提出了一种基于单相半桥子模块(HBSM)的预充电策略。该策略的第一阶段仍为不控整流,第二阶段通过上下桥臂的能量之和与能量之差的控制来实现子模块电容的boost升压。之后,直流侧电容电压被交流侧持续馈入的能量充到额定值。该控制方案使整个启动过程快速、平滑、稳定,对单相MMC做整流运行具有重大价值。最后,所提方案的有效性及正确性在一台单相8个子模块的实验样机上得到了验证。