【作者】 孙绍华；

【导师】 贲洪奇；

【作者基本信息】 哈尔滨工业大学 ， 电力电子与电力传动， 2015， 博士

【摘要】 随着太阳能、风能等可再生能源并网发电技术的发展,PWM逆变器因具有网侧电流正弦化、单位功率因数、能量双向流动、能够实现电能的“绿色变换”等优点受到广泛应用。然而,在不平衡电网条件下,逆变器中具体存在下面几个问题需要解决:传统的锁相方法在电网发生不平衡时存在锁相精度差、动态响应慢的缺点;按照电网平衡状态运行的逆变器,当电网发生不平衡时并网电流中含有大量的谐波,不能满足GB/T 14549-1993《电能质量公用电网谐波》中规定的注入公用电网的谐波电流分量允许值;为了避免桥臂直通,需要在逆变器开关管控制信号之间加入死区时间,因而造成了死区效应,导致并网电流中谐波含量增加。为了有效解决上述问题,本文以三相电压型并网逆变器为研究对象,对其相关问题进行了深入研究。并网逆变器中,电网信号的快速准确获取是并网逆变控制的关键。电网电压不对称且含有谐波的不平衡电网条件下,传统的基于信号延时对消(DSC)技术的锁相方法存在锁相精度差、动态响应慢的缺点。为此,提出一种基于快速正负序分离(FPNSD)算法的锁相方法,并分析了FPNSD算法的工作机理,进行了仿真分析和实验验证。结果表明,所提出的基于FPNSD的锁相方法可以消除电网电压中谐波对锁相精度造成的影响,有效提高锁相精度和速度。基于DSC的传统锁相方法和基于FPNSD的锁相方法,均要求电网频率是固定的。当电网频率发生变化时,上述两种方法均不能正常工作。为此,在分析自适应陷波器(ANF)工作机理的基础上,提出一种基于FPNSD-ANF的频率自适应锁相方法,借助ANF的频率自适应单元及时更新基于FPNSD算法中的电网频率,实现了不平衡电网条件下电网频率的自动跟踪。仿真分析和实验结果表明,提出的自适应锁相方法不仅实现了频率变化时的锁相,具有良好的动态性能,且结构上不需要压控振荡器,因此具有结构更加简单的优点。不平衡电网条件下的功率补偿控制策略,需要利用电流正序分量进行补偿功率的计算,因此电流正序分量提取的准确性就直接影响到功率补偿的准确性。常用的基于瞬时无功功率理论的谐波电流提取方法,存在动态响应慢和无法实现特定次谐波提取的缺点。为此,在详细分析电网不平衡时逆变器谐波电流产生机理的基础上,提出一种基于多通道ANF的谐波电流提取方法。该方法可以为并网逆变器不平衡电网条件下的功率补偿、特定次谐波抑制等应用场合提供准确的参考信号。最后通过实验验证了算法的有效性。为了改善并网逆变器在不平衡电网条件下的运行性能,利用瞬时功率理论进行了逆变器功率脉动及功率补偿控制效果分析。在此基础上,为了减少并网逆变器对电网注入的二倍频功率脉动,基于直接功率控制、提出一种改进的功率补偿控制策略,改进后的功率内环中禁止电压负序分量参与功率内环调节。仿真分析和实验结果表明对功率内环进行改进后,在实现无负序电流注入电网、输出有功功率无二倍频脉动和输出无功功率无二倍频脉动等3种不同控制目标的同时,提高了补偿功率精度,降低了并网电流THD,极大的改善了并网逆变器的运行性能。逆变器开关控制信号之间加入死区时间后,控制电压中产生的误差电压导致并网电流发生畸变。为了减少死区造成的影响,在进行逆变器死区效应分析的基础上,将死区时间进行在线调整,提出一种基于指数趋近律的快速终端滑模死区补偿策略。分析了快速终端滑模控制的原理、进行了滑模控制器的设计,利用Levant微分器替代滑模控制器中的微分运算,增强了滑模控制器的抗噪声干扰能力。该方法无需电流极性检测、无需电流PARK变换,在实现死区补偿的同时,简化了控制系统结构,提高了系统的鲁棒性。最后通过实验验证了理论分析的正确性。更多还原

【Abstract】 With the development of grid-connected technology of renewable energy such as solar energy and wind energy, PWM inverter is widely used considering its various advantages such as grid-side current sinusoidal, unit power factor, bidirectional energy flow and green transformation of electrical energy. However, under unbalanced grid conditions, the following problems existed in inverter should be solved: the accuracy of the tranditional phase locked method is low, and the dynamic response speed is slow; under unbalanced grid conditions, there are large numbers of harmonic currents in inverter operating with balanced control strategy, which cannot meet the demand of the allowable value of harmonic currents into the utility grid specified in GB/T 14549-1993 Quality of Electric Energy Supply-Harmonics in Public Supply Network. In order to avoid arm short-through, dead-time must be added between the contol signals of power switchings, which causes dead-time effect and the increasing of harmonic contents of grid-connected currents. This paper takes the three-phase voltage source grid-connected inverter as the research object, makes further study and offers better solutions of above related problems.The rapid and exact acquisition of grid signal is the key of grid-connected control. Under unbalanced and harmonic polluted grid conditions, tranditional phase locked method based on deleyed signal cancellation(DSC) technique has shortcomings of low accuracy and slow dynamic response speed, so a fast positive and negative sequence decomposition(FPNSD)-based phase locked strategy is proposed, and its operational principle is analyzed. The simulation and experimental results show that the proposed phase locked method can eliminate the impact of the grid harmonics, and improve the phase locked speed and accuracy.Both tranditional DSC-based and FPNSD-based phase locked methods demand that the grid frequency is time-unvaried, so these two methods are invalid when the grid frequency changes. Based on the theory analysis of adaptive notch filter(ANF), a novel adaptive phase locked method based on FPNSD-ANF is proposed. It uses the frequency adaptive unit of ANF update the frequency of FPNSD, which realizes the tracking of the grid frequency under unbalanced grid conditions. The simulation and experimental results show that the proposed algorithm with high dynamic performance can track the grid frequency, and the proposed method does not need voltage-controlled oscillator, which makes its structure much simpler.Power compensation control strategy under unbalanced grid conditions needs the positive current component to compute the compensating power, so the accuracy of the extracted positive current component impacts the accuracy of the power compensation. The widely used harmonic current extraction method based on instantaneous reactive power theory, is unable to realize a selective order harmonic extraction, and its dynamic response speed is slow. Based on the theory analysis of the harmonic current generation of inverter under unbalanced grid conditions in detain, a parallel ANF-based harmonic current extraction method is proposed. The main function of this harmonic current extraction method is to provide accurate reference signal for power compensation of inverter under unbalanced grid conditions and elimination of certain harmonics applications. Finally, the validity of theoretical analysis is proved by experimental results.To improve the grid-connnected inverter performance under unbalanced grid conditions, power ripple and control effect of power compensation are analyzed using the theory of instantaneous power. To reduce double frequency power ripple pulsating into grid, a modified power compensation control stratrgy is proposed based on direct power control, the negative voltage component is prohibited in the inner power loop. The simulation and experimental results show that the modified power compensation control strategy realizes three targets, namely obtaining the grid-connected current without negative component, removing reactive double frequency power ripple and cancelling the active double frequency power ripple. At the same time, the new control strategy improves the precision of compensation power, reduces the grid-connected current THD, and greatly improves the performance of inverter.Dead-time added between the control signal of power switching causes errors in the control voltage, which leads to the grid-connected current distortion. To weaken the impact of dead-time, based on the analysis of dead-time effect of inverter, the dead-time is adjusted on line, and dead-time compensation of inverter based on an exponent approaching law with fast terminal sliding mode controller is proposed. Then fast terminal sliding mode theory is introduced and sliding mode controller is designed; in the controller, the differential operation of the sliding mode controller is replaced by Levant differentiator, which enhances the sliding mode controller’s ability of noise resistance. The novel dead-time compensation method without current polarity detecting and current PARK transfomation simplifies the system structure, and improves the robustness of the system. Finally, the correctness of theoretical analysis is verified by experimental results.更多还原