摘要
模块化多电平换流器(MMC)子模块(SM)发生故障时,快速检测到故障并定位故障SM是提升MMC可靠性的关键。现有研究基于经验的阈值设置在不同运行功率间难以推广。针对于此,提出一种适用于不同运行功率的最近电平调制(NLM)策略下MMC子模块开路故障诊断策略。所提策略通过判断SM电容电压预测值与实际值间的绝对误差是否超出阈值来检测并定位故障。通过数学推导给出了设置阈值的可靠依据,并验证了当运行功率发生改变时无需重新手动设置阈值,与现有研究相比降低了阈值设置难度。此外,所提策略整合了现有策略的优点,包括无需额外硬件,计算负担小,诊断速度快(<20ms),适用于多个SM发生故障的情形等。同时,通过理论分析验证了所提策略不仅适用于NLM策略的情形,在调整SM开关函数的预测方法后可推广至其他MMC调制策略。在硬件在环平台中的实验结果验证了该策略可以在不同功率点准确、快速地诊断出两种MMC子模块开路故障。
With the increasing voltage and power level of modular multilevel converters(MMC),the number of its submodules(SMs)also increases,and the issue of its reliability is highlighted.The failure of IGBT in any SM can affect the normal operation of MMC and even further lead to the damage of other components,which eventually lead to the collapse of the whole system.Thus,it is necessary to detect the fault and locate the malfunctioning SMs accurately to improve its reliability.MMC’s SM open-circuit diagnosis strategy can be divided into two categories:hardware-based and software-based.Compared with the hardware-based strategy,the software-based strategies need no extra hardware,have low computational burden.However,it is difficult to set the empirical threshold of existing software-based strategies between different operating powers,which hinders its further development.To solve this issue,a diagnosis strategy for open-circuit SM faults in MMCs suitable for different operating powers is proposed.The SM switching function is predicted based on the number of SM inputs and the position of SM capacitor voltage sorting arrangement and then the corresponding SM capacitor voltage is predicted.On the basis,the fault is detected and located by judging whether the absolute error between the predicted value and the actual value of the SM capacitor voltage exceeds a threshold.Moreover,to further eliminate the effects of errors and prevent the existence of fault misdiagnosis situations,a time flag is used in both the detection process and location process.In the proposed strategy,to avoid the effects of misdiagnosis near the arm current-over-zero point,a current-over-zero filtering part is proposed.Based on the mathematical deduction,the principle of setting threshold is given.It is indicated that the proposed strategy eliminates the need to manually set the threshold when the MMC operating power changes,which greatly reduce the difficulty of setting the threshold compared with the existing strategies.At the same time,theoretical analysis verifies that the proposed strategy is not only suitable for NLM modulation strategy,but also can be extended to other MMC modulation strategies after adjusting the prediction method of SM switching function.A detailed real-time digital simulation model of the MMC-HVDC system is built in a hardware-in-the-loop platform.The power-stage model is emulated by the target machine and the control system is realized by the DSP TMS320F28335 control board.The experimental result verify that the proposed strategy can accurately diagnose two types of MMC SM open-circuit faults at different operating powers.It is observed that the absolute error of a Type I malfunctioning SM is high when the arm current is negative and the absolute error of a Type II malfunctioning SM is high when the arm current is positive,which verifies the correctness of the theoretical analysis.Before the fault occurs,the absolute error will not exceed the threshold so that misdiagnosis will not occur during normal operation.After the fault occurs,the absolute error exceeds the threshold,the system can quickly detect the fault and then locate the remaining malfunctioning SMs.Moreover,the proposed strategy integrates the advantages of existing strategies,including no extra hardware,low computational burden,fast diagnosis(<20 ms),and can cope with the cases of multiple SM failures in the arm.
作者
武鸿
王跃
薛英林
刘熠
李鹏坤
Wu Hong;Wang Yue;Xue Yinglin;Liu Yi;Li Pengkun(State Key Laboratory of Electrical Insulation and Power Equipment,Xi’an Jiaotong University,Xi’an 710049,China;State Power Economic Research Institute,Beijing 102209,China)
出处
《电工技术学报》
EI
CSCD
北大核心
2024年第1期233-245,302,共14页
Transactions of China Electrotechnical Society
基金
国家电网公司科技项目资助(5100-202156434A-0-0-00)。
