基于电压型换流的矩阵变换器输出电压补偿方法

分析矩阵变换器电压型两步换流过程导致的输出电压误差,着重分析开关管寄生电容对换流过程电压误差的影响,并提出一种补偿方法。指出开关管寄生电容的充放电过程会导致开关管在关断时管压降上升时间延长,在负载电流较小的情况下导致实际输出电压误差小于理论输出电压误差。给出考虑开关管寄生电容后电压型两步换流过程导致的输出电压误差的通用表达式。在考虑开关管的通态压降后给出一种对输出电压的补偿方法,该方法不仅可消除矩阵变换器各种非线性因素导致的输出电压波形畸变,并且可使期望输出电压与实际输出电压相符。开环阻感负载实验及感应电机低速运行矢量控制实验证明了补偿方法的正确性。

矩阵变换器电压型换流技术研究

矩阵式变换器(Matrix Converter,简称MC)作为一种新型AC/AC直接变换器逐渐成为国内外研究的热点。在较为详细地分析和阐述MC电压型两步换流技术的基础上,针对临界区域内电压检测不准确易导致换流失败的问题提出了改进措施,采用状态机的设计方法编写了基于VHDL语言的CPLD换流程序,并在实验装置上进行了验证。仿真和实验结果证明了理论的正确性。

矩阵变换器的电压型换流策略研究

矩阵变换器由于换流困难始终无法在大功率环境中得到推广应用,本文在传统的电压型两步换流法的基础上,提出了一种电压型两步换流策略。该方法通过调整矢量顺序避免了电压接近的输入相之间的换流,解决了原来换区间时输入相容易短路的现象,完善了电压型换流策略。该策略不仅对输入输出波形影响较小,而且实现较为简单,系统开关损耗也不会发生变化。输出实验表明,该换流策略是可行的,所提出的新型换流策略可以在大功率交-交电力变换中得到进一步推广和应用。

矩阵变换器的电压型两步换流策略

分析了基本的电压型两步换流策略,在输入两相电压值接近(电压换区间)时刻,由于输入相电压的相对大小判断错误而导致输入相的短路现象以及原因。为此,提出了基于电压型两步换流策略的矩阵变换器控制方法,通过引入过渡区间,并在过渡区间内定义新的P、M、N状态和PM、MN、NP暂态以及调整过渡区间中每个调制周期的零矢量和双向功率开关状态换流次序,可以避免输入相电压在过渡区间因判断不准确而出现的短路现象,实现矩阵变换器安全、可靠的两步换流和稳定运行,且输出电压波形和输入电流波形不受影响。在5kW矩阵变换器实验样机上进行了大量的实验,实验结果表明,所提出的控制方法可实现矩阵变换器电压型两步换流和安全运行,而不需要外加专门的精确检测输入相电压相对大小关系的测量装置,控制电路简单易行。

矩阵变换器电压型两步换流策略及实现

针对电压型换流策略在输入线电压过零区域,由于测量不准确会导致短路,本文提出了基于临界区域的两步换流策略。通过在临界区域中定义新的P、M、N状态和PM、MN、NP暂态以及调整临界区域中每个调制周期的零矢量和双向功率开关状态换流次序,可以避免输入相电压在临界区域因判断不准确而出现的短路现象,且输出电压波形和输入电流波形不受影响。并据此研制了一台5kW矩阵变换器原理样机,采用FPGA实现了电压区间检测和换流控制逻辑,并详细给出了FPGA的换流控制时序。实验结果表明,该方法不需要精确的测量电路即可实现矩阵变换器安全、可靠的两步换流。

矩阵变换器的一种安全换流策略

矩阵变换器由于换流困难始终无法在大功率环境中得到推广应用,该文在传统的电压型两步换流法的基础上,提出一种过渡区间采用四步换流的安全换流策略,在电压接近的换流两相之间插入3个安全续流状态来实现换流,避免了电流型换流法小电流检测困难的问题,解决了原来换流法换区间时容易短路的现象,完善了电压型换流策略。该策略不仅对输入输出波形影响较小,而且实现较为简单,系统开关损耗也不会增长很多。全压380V输入和5kW功率输出实验结果表明,该换流策略是可行的。提出的新型换流策略可在大功率交–交电力变换中得到进一步推广和应用。

矩阵变换器输入功率因数可调时的换流控制策略

矩阵变换器的电压型两步换流策略具有换流过程快,开关损耗小,不受运行工况影响,控制系统结构简单等优点。针对该方法在输入电压换区间时易发生短路的现象,一些文献提出了一种带有过渡区间的电压型两步换流策略,较好地解决了矩阵变换器在较大功率输出条件下的换流问题,但是该方法只适用于输入功率因数为1附近的情况,当输入功率因数变化较大时,系统仍会发生短路问题。为此,本文在具体分析换流过程的基础上,提出了适用于输入功率因数可调时的换流方法,在过渡区间内通过判断电压的相对大小,使用换序法将大压差电压调整至调制顺序的中间,避免了换流时可能出现的短路现象,进一步完善电压型两步换流策略。最后,仿真和实验结果表明本文所提出的改进策略是正确可行的。

Adaptive controller design based on input-output signal selection for voltage source converter high voltage direct current systems to improve power system stability

An input-output signal selection based on Phillips-Heffron model of a parallel high voltage alternative current/high voltage direct current(HVAC/HVDC) power system is presented to study power system stability. It is well known that appropriate coupling of inputs-outputs signals in the multivariable HVDC-HVAC system can improve the performance of designed supplemetary controller. In this work, different analysis techniques are used to measure controllability and observability of electromechanical oscillation mode. Also inputs–outputs interactions are considered and suggestions are drawn to select the best signal pair through the system inputs-outputs. In addition, a supplementary online adaptive controller for nonlinear HVDC to damp low frequency oscillations in a weakly connected system is proposed. The results obtained using MATLAB software show that the best output-input for damping controller design is rotor speed deviation as out put and phase angle of rectifier as in put. Also response of system equipped with adaptive damping controller based on HVDC system has appropriate performance when it is faced with faults and disturbance.

Research on the control method for voltage-current source hybrid-HVDC system

The hybrid-HVDC topology,which consists of line-commutated-converter(LCC)and voltage source converter(VSC)and combines their advantages,has extensive application prospects.A hybrid-HVDC system,adopting VSC on rectifier side and LCC on inverter side,is investigated,and its mathematic model is deduced.The commutation failure issue of the LCC converter in the hybrid-HVDC system is considered,and a novel coordinated control method is proposed to enhance the system commutation failure immunity.A voltage dependent voltage order limiter(VDVOL)is designed based on the constant DC voltage control on the rectifier side,and constant extinction angle backup control is introduced based on the constant DC current control with voltage dependent current order limiter(VDCOL)on the inverter side.The hybrid-HVDC system performances under normal operation state and fault state are simulated in the PSCAD/EMTDC.Then,system transient state performances with or without the proposed control methods under fault condition are further compared and analyzed.It is concluded that the proposed control method has the ability to effectively reduce the probability of commutation failure and improve the fault recovery performance of the hybrid-HVDC system.