【作者】 王树文；

【导师】 纪延超；

【作者基本信息】 哈尔滨工业大学 ， 电力系统及其自动化， 2009， 博士

【摘要】 交流/直流/交流(AC/DC/AC)电压源变换器已在民用、工业、军事等领域被广泛使用,引起了国内外专家、学者的广泛关注。随着社会对电能需求以及电力用户对高质量、高可靠性电源系统需求的日益增长,对交直交电压源变换器的输入输出性能等方面提出了更高的要求。由此,交直交电压源变换器直流侧大容量电解电容所带来的负面效应受到了高度重视。大容量电解电容的使用导致变换器占用空间大、成本高,给电网带来了严重谐波污染和相关电能质量问题,且在多数情况下,电容的使用寿命是限制变换器使用寿命的主要因素。因此,采用新颖的拓扑结构与合理有效的调制技术来提高交直交电压源变换器的输入输出性能也就成为国内外学者研究的重要问题。本文正是针对不同负载情况下新型交直交电压源变换器的调制技术以及过电压保护方法等方面进行了一系列研究。文中提出了新型交直交电压源变换器的拓扑结构,建立了其数学模型,同时分析了直流侧电压的波动情况以及网侧电流谐波情况。数学模型的建立为谐波分析、直流侧过电压抑制、调制技术研究奠定了理论基础。由分析可知:直流侧电压的波动是由整流桥和逆变桥共同作用引起的;网侧电流的总谐波畸变率随着直流侧电容的容量增大而增大。输出高质量的电压是新型交直交电压源变换器的重要功能之一。但是,采用新的拓扑结构后三相不可控整流桥会输出波动的直流电压,而在直流侧电压波动情况下,仍采用传统的SPWM调制技术就会使其输出电压中含有大量的低次谐波,对负载产生不利影响。针对该问题,文中提出一种改进的重构调制波正弦脉宽调制(ARMW-SPWM)技术,该调制技术的使用可以更好地消除阻感负载情况下直流侧电压的波动对新型交直交电压源变换器输出电压中产生低次谐波的影响,同时可以显著地减小直流侧电容的容量,从而简化了变换器主电路。文中通过仿真验证了其理论分析的正确性。在标量控制的变频调速系统中,变换器输出准确的电压矢量是非常重要的。电动机负载情况下,仍采用传统的SVPWM技术调制新型交直交电压源变换器,就会使其输出电压矢量与参考电压矢量产生误差,这样对电动机就不能正确控制。因此本文提出了磁链差分空间矢量脉宽调制(FLDSVPWM)技术,该调制技术能够使新型交直交电压源变换器输出正确的电压矢量。另外,由于直流侧电压的波动,使新型交直交电压源变换器的线性调制区域结束的比较早。由此,本文提出了幅值恒定过调制(ACOM)技术,从而使新型交直交电压源变换器可以获得较高输出调制比。新型交直交电压源变换器的过电压与谐振的抑制对于提高其可靠性、网侧性能至关重要。在轻载或电动机回馈制动的时候,功率流从电机回馈到直流侧,可导致新型交直交电压源变换器直流侧过电压。由于传统的过电压保护方法是基于理想的直流侧电压进行过电压保护的,但是在新型交直交电压源变换器中,直流侧电压是波动的,所以传统的过电压保护方法不再适用。针对该问题本文提出了功率因数动态跟踪控制(PFDTC)直流侧过电压保护新方法,该方法能够提前判断电动机的回馈制动状态,从而有效地抑制能量回馈避免过电压的产生。另外,由于直流侧电容容量以及网侧滤波器阻抗值的减小,使直流侧电容与网侧电抗的谐振频率增高与开关频率接近甚至超过开关频率,所以容易产生谐振,对网侧产生不利影响。针对此问题本文通过仿真和实验确定了避免谐振的条件,从而抑制谐振的发生。新型交直交电压源变换器的设计与实验。本文详细论述了新型交直交电压源变换器的实验系统方案。针对控制任务的特点,采用了高性能DSP主控系统和单片机监控系统的复合架构,达到了高速实时控制与友好人机界面的统一。最后从实验系统的测量结果表明:理论分析正确、实验方案可行,为进一步研究奠定了重要的理论和实践基础。更多还原

【Abstract】 AC/DC/AC voltage source converter (VSC) widely used in civil, industry or military territory becomes research focus of scholars and experts from home and abroad. With the demand of power energy and the request of consumers to high quality and reliable power increasingly getting higher, AC/DC/AC VSC is starving for improvement in input and output performance. However, its high capacitance DC capacitor brings negative effect which is noticed today. The equipment that uses high capacitance electrolytical capacitor has disadvantages, such as bulk, high price, heavy harmonic pollution and relating power quality problem. In many cases, the lifetime of the capacitor is main factor limiting lifetime of the converter. So, novel topology and modulation technique of AC/DC/AC VSC is a difficult task to scholar engaged in this field. Due to above-mentioned problem, a series research work on modulation technique and overvoltage protecting method for novel AC/DC/AC VSC under different loads is carried out.A novel AC/DC/AC VSC main circuit topology is proposed and system mathematic model including DC side and inverter-bridge is estabished and fluctuating situation of DC side voltage and harmonic of line side current are detailedly analyzed. Foundation of mathematic model provides important theoretic basis for harmonic analysis and suppression of DC side overvoltage and research of modulation strategies. Analysis results show that DC side voltage fluctuation can be estimated by summing fluctuations due to the rectifier and inverter-bridge and the higher of DC side capacitor capacitance, the larger of THD for line side current.Producing high quality voltage is one of novel AC/DC/AC VSC’s important functions. However, uncontrolled rectifier for new topology outputs ripple DC voltage. As ripple DC voltage, low harmonics of output voltage are largely increased by using traditional moudlation technique so as to produce adverse effect to load. Due to above-mentioned problem, an advanced reconstruction modulation wave SPWM (ARMW-SPWM) technique is proposed. Investigation results show proposed technique can eliminate harmonics caused by ripple DC voltage for output voltage under resistance inductance load and can greatly reduce DC capacitor so that main circuit are simplified. The ARMW-SPWM technique theory analysis is verified by simulation.It is very importance of producing correct voltage vector for converter under variable speed drives system of scalar control. Because of the constant DC side voltage assumption during the switching period leads to an error in produced voltage for novel AC/DC/AC VSC so that the electromotor cann’t be accurately controlled. So the new modulating principle, named Flux Linkage Differential Space Vector Pulse Width Modulation (FLDSVPWM), is proposed in the basis of Space Vector Pulse Width Modulation (SVPWM). Investigation results show FLDSVPWM technology used is able to produce the correct voltage vector. On the other hand, Due to DC side voltage fluctuation, the linear modulation region ends earlier compared with a high capacitance DC-link capacitor VSC. So, Amplitude Constant Overmodulation (ACOM) technique is proposed that can make converter’s output modulation index achieve higher.It is very importance of suppressing overvoltage and resonance for novel AC/DC/AC VSC to improve its reliability and line side performance. When motor is light load or braking, power direction is changed from converter to motor so as to make DC side voltage raise intolerably high. Traditionally, the DC side overvoltage protection has been carried out by ideal nonripple DC side voltage. But DC side voltage for novel AC/DC/AC VSC is by far not constant and fluctuates rapidly so that traditonal overvoltage protecting method cann’t be used. To solve this problem, a new DC side overvoltage protection method, named PFDTC, based on power factor dynamic tracing control has been introduced. The method can ahead judge braking state of electromotor and suppress the energy back to avoid the overvoltage. Otherwise, due to small DC side capacitor and samll line side impedence, the resonance frequency between DC side capacitor and line side inductance becomes significantly high getting close to or even exceed the switching frequency that easily result in resonance. The approximate margin to avoid the resonance is decided by simulation and experiment so that adverse effect from resonance is suppressed.Novel AC/DC/AC VSC is designed and experimented. The experimental prototype of novel AC/DC/AC VSC is discussed in detail. Especially, multiple configuration controller buildup with high performance DSP system and C51 platform is developed according to the character of control tasks. Hence high speed real-time control and friendly human interface is combined. Finally, the results obtained from experimental system prove the validity and feasibility of novel AC/DC/AC VSC, which gives important theortical and practical foundation for further research.更多还原