风力发电并网侧滤波器研究

发布时间：2019-01-09 14:05

【摘要】：风力发电系统的核心部分就是并网逆变器,逆变器对于风力发电机而言,相当于是非线性负载,能够带来大量的谐波,因此在风力发电系统中,尤其网侧滤波器是不可或缺的。并网逆变系统的后级输出滤波器有三种类型:L、LC、LCL。比较三者的滤波性能,可以发现在开关频率比较低的并网逆变系统中,L、LC滤波器需要较大的电感量才能满足对高次谐波的滤波要求,成本较高。由于高次谐波衰减特性好以及所需较小电感等特点,LCL滤波器在并网逆变系统中逐渐替换了传统的L、LC滤波器。但是LCL滤波器的引入,会给系统带来谐振问题,需要采用适当的控制策略来解决这一问题。所以本文以LCL滤波器并网逆变系统为研究对象,研究了在理想电网电压和不平衡电网电压两种情况下的电流控制策略。本文首先对LCL滤波器进行了分析设计,然后建立了LCL滤波并网逆变系统在理想电压条件和不平衡电网条件下数学模型。在理想电压条件下,分别研究了网侧电流反馈和逆变器侧电流反馈控制策略。针对LCL滤波器的谐振问题,讨论有源阻尼法和无源阻尼法的抑制效果。无源阻尼法易于实现,但增加了系统成本;有源阻尼可以较好地抑制谐振峰,然而控制却变得复杂,且参数偏差和逆变器的开关频率表都会制约有源阻尼法。在此基础上,基于抵消控制系统传递函数零极点的思路,就提出了“LCCL”电流反馈控制策略,让并网逆变控制系统将由三阶降阶为一阶。相对于前面的传统电流反馈控制方法,该方法不需要复杂的计算,可以让控制回路的极点增益大大削弱,使系统运行效率得到提高。当实际系统运行在不平衡电网条件时,“LCCL”电流反馈控制策略不一定能够适用,所以需要研究不平衡电网条件下的控制策略。本文针对传统控制策略在不平衡电网条件下瞬时功率特性方面的问题,提出了协调控制瞬时功率波动与入网电流的幅值不平衡策略。然后对比分析采用PIR(比例积分谐振)和PI(比例积分)控制器的并网逆变系统对谐振的抑制效果和静差的消除效果。发现在不平衡电网电压下,不论低频,还是高频,采用PIR控制器,滤波效果都比较好。但是引入谐振控制器,会将提高系统控制复杂程度,于是提出电网电压前馈并结合逆变器侧电流反馈的无阻尼控制策略,能够消除入网电流受电网电压的控制影响。通过在Matlab/Simulink仿真中对该策略进行验证,发现在不平衡电网电压条件下,加入电网电压前馈的控制系统中入网电流波形仍然呈现对称状态,没有发生变化,降低谐波污染。
[Abstract]:The core part of wind power system is grid-connected inverter. The inverter is equivalent to nonlinear load for wind turbine and can bring a lot of harmonics, so in wind power system, especially grid-side filter is indispensable. There are three types of output filter in grid-connected inverter system: LLLC / LCL. By comparing their filtering performance, it can be found that in grid-connected inverter systems with low switching frequency, large inductance is needed to satisfy the requirements of high-order harmonic filtering and the cost is high. Due to the characteristics of high harmonic attenuation and small inductance, the LCL filter is gradually replaced by the traditional LLC filter in the grid-connected inverter system. However, the introduction of LCL filter will bring resonance problem to the system, which needs to be solved by appropriate control strategy. So this paper takes the LCL filter grid-connected inverter system as the research object and studies the current control strategy under the condition of ideal grid voltage and unbalanced network voltage. In this paper, the LCL filter is first analyzed and designed, and then the mathematical model of LCL filter grid-connected inverter system under ideal voltage conditions and unbalanced grid conditions is established. Under the ideal voltage condition, the control strategies of grid-side current feedback and inverter side current feedback are studied respectively. Aiming at the resonance problem of LCL filter, the suppression effect of active damping method and passive damping method is discussed. The passive damping method is easy to realize, but it increases the system cost. The active damping method can suppress the resonant peak well, but the control becomes complex, and the parameter deviation and the switching frequency meter of the inverter will restrict the active damping method. On this basis, based on the idea of zero pole of the transfer function of canceling control system, a "LCCL" current feedback control strategy is proposed, which will reduce the third order to the first order of the grid-connected inverter control system. Compared with the traditional current feedback control method, this method does not require complicated calculation, and it can greatly weaken the pole gain of the control loop and improve the efficiency of the system. The "LCCL" current feedback control strategy may not be applicable when the actual system is running under unbalanced power network conditions, so it is necessary to study the control strategy under unbalanced power network conditions. In order to solve the problem of instantaneous power characteristics in unbalanced power network with traditional control strategy, a coordinated control strategy is proposed to control the amplitude imbalance between instantaneous power fluctuation and incoming current. Then the resonance suppression effect and static error elimination effect of grid-connected inverter system with PIR (proportional integral resonance) and PI (proportional integral) controller are compared and analyzed. It is found that the filtering effect is better by using PIR controller under unbalanced grid voltage, whether low frequency or high frequency. However, the introduction of resonant controller will increase the complexity of the control system. Therefore, an undamped control strategy based on feedforward voltage feedforward and inverter side current feedback is proposed, which can eliminate the influence of grid voltage on incoming current. Through the verification of the strategy in the Matlab/Simulink simulation, it is found that under the condition of unbalanced grid voltage, the input current waveform of the control system with feedforward voltage of the power network still presents symmetrical state, no change, and the harmonic pollution is reduced.
【学位授予单位】：上海电机学院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM614;TM761

【参考文献】