基于LCL滤波的微网逆变器控制策略研究

发布时间：2018-04-01 09:47

本文选题：LCL滤波器　切入点：微电网　出处：《大连理工大学》2014年博士论文

【摘要】：随着新能源的广泛应用,我国分布式发电系统得到了快速发展,由分布式发电系统组成的微电网系统越来越受到世界的关注。基于LCL滤波的微网逆变器控制策略的研究对于保障微电网的安全运行,具有十分重要的工程实际意义,其关键性技术为：抑制LCL滤波器谐振尖峰的控制技术；电网不平衡状态下网侧电流控制技术、电网电压有效值与同步相位检测算法；解决微电网中分布式发电系统无功功率分配不准确问题的无功功率下垂系数校正技术。本文围绕关键技术,对基于LCL滤波器的微网逆变器的控制策略开展理论与实验研究,研究成果可以应用到实际工程中,对微电网的高效运行具有一定的理论指导意义与实用价值。本文分别建立了三相静止坐标系、两相静止坐标系以及两相同步旋转坐标系下的基于LCL滤波的微网逆变器数学模型。基于所建立的数学模型,分析LCL滤波器的谐振特性,并提出抑制谐振尖峰的方法。通过与被动阻尼法比较,分析采用电容支路电流反馈代替连接阻尼电阻的方法和控制策略。针对其控制策略复杂的问题,在详细分析电网侧电流反馈与逆变器侧电流反馈闭环控制系统的内在联系基础上,给出逆变器侧电流反馈等效为电网侧电流反馈加入电容支路电流反馈的有源阻尼的方法即无阻尼控制策略,避免了在电容支路增加电压或电流传感器的问题,同时也简化了微网逆变器控制策略,为后续电网不平衡状态下微网逆变器控制策略的研究提供理论基础。电网不平衡会对微网逆变器网侧电流的控制、电网电压有效值与同步相位的计算与检测产生严重影响,造成逆变器工作异常,严重时损坏逆变器。本文在分析电网不平衡对微网逆变器控制影响的基础上,采用PI控制器加入谐振(R)控制器的方法,调节电压负序分量引起的100Hz交流量静差。由于谐振控制器的加入,使微网逆变器的控制策略复杂化,为了避免增大系统控制复杂程度。本文提出电网电压前馈的控制策略,将电网电压前馈到控制回路中,实现消除电网电压对网侧电流控制的影响,进而消除电压负序分量对网侧电流的影响。电网电压有效值的计算方面,本文提出基于低通滤波器的电压有效值计算方法,该方法只需一个瞬时电压采样值就可以得出电网电压有效值,相对于全周期采样法、导数法以及迭代法更加的便捷,并且适用于电网不平衡状态。电网不平衡对电网电压同步相位的检测具有严重影响,本文提出一种电网基波正序电压的提取方法,运用数学变换方法能够在电网不平衡甚至畸变状态下,提取基波正序分量,从而进行电压同步相位检测控制。该算法通过两次数学变换消除电压负序及谐波分量,得到基波正序电压分量,避免了谐振控制器的加入,减小系统复杂度。对电网不平衡状态下微网逆变器控制策略的研究,为实现微电网具有应对电网电压跌落和系统不平衡的能力的运行要求提供了理论支持。本文通过分析下垂控制的原理,针对下垂控制有功、无功功率不能够完全解耦、无功功率分配不准确等问题,提出微电网逆变器下垂控制系数校正算法,与虚拟阻抗控制算法有机结合,达到有功、无功功率完全解耦提高无功功率分配准确度的效果。仿真结果有效验证这种方法的正确性与可行性。最后,本文研制容量为250kVA的基于LCL滤波的微网逆变器样机,该逆变器采用低通滤波器法计算电网电压有效值,数学变换方法获取电网电压同步相位,并且运用电压前馈控制与无阻尼控制相结合的控制策略,实现无功功率补偿、黑启动、联网运行模式切换到孤岛运行模式、根据用户需求对储能器件蓄电池进行恒功率、恒电压、恒电流多种策略充放电、电网不平衡时对网侧电流有效控制等功能。在所研制样机的基础上,进行多种工况的实验研究,实验结果证明了本文所提微网逆变器控制策略的有效性与正确性。
[Abstract]:With the wide application of new energy, distributed power generation system in China has been rapid development, composed of distributed power generation system of micro grid system more and more attention of the world. The safe operation of microgrid inverter control strategy for the protection of LCL filter based on micro grid, has very important practical significance, and its key technology as control technology to inhibit LCL filter resonance peak; unbalanced grid state grid side current control technology, power grid voltage value and synchronous phase detection algorithm; to solve the reactive power droop coefficient correction technology in micro grid distributed power system reactive power distribution is not accurate. This paper focuses on key technologies, on the theory and experimental study on the control strategy of microgrid inverter based on LCL filter, the research results can be applied to the actual project, efficient transport of micro grid It has a certain theoretical guiding significance and practical value.
This paper established the three-phase static coordinate system, two-phase stationary coordinate system and the two-phase synchronous rotating coordinate system of the micro grid inverter mathematical model based on LCL filter. Based on the mathematical model, the analysis of resonant LCL filter, and puts forward the method of inhibiting the resonant peak. By the comparison and analysis of passive damping method, using capacitor branch current feedback control strategy and method instead of connecting damping resistance. The control strategy of complex problems in a detailed analysis of the grid side current feedback and the inverter side current feedback loop control system based on the internal relations, gives the inverter side current feedback method is equivalent to the grid side current feedback capacitor with active damping of the branch current feedback no damping control strategy, to avoid increasing the voltage or current sensor in the capacitor, but also simplifies the microgrid inverter control The strategy provides a theoretical basis for the study of the control strategy of the microgrid inverter in the unbalance state of the power grid.
Unbalanced grid to control micro grid inverter grid side current, grid voltage effective value calculation and seriously affect detection and phase synchronization, resulting in inverter disorder, serious damage. The inverter based on the analysis of the power imbalance on the basis of microgrid inverter control. The effects of using PI controller (R) with resonant controller the 100Hz method, AC voltage regulation of negative sequence components caused by static error. Due to the resonant controller, the control strategy of micro grid inverter is complicated, in order to avoid increasing the complexity of system control. The proposed control strategy for grid voltage feed-forward, the grid voltage feedforward control loop to eliminate the voltage on. The impact of the net side current control, and eliminate the influence of voltage negative sequence components of the grid current. The calculation of the effective value of the voltage of the power network, this paper based on the low-pass filter The calculation method of effective value of voltage, this method only needs an instantaneous voltage sampling value can be drawn on the effective value of voltage, relative to the full period sampling method, derivative method and iterative method is more convenient, and is suitable for the unbalanced state. The power imbalance has severely affected the detection of grid voltage synchronization phase, is proposed in this paper. An extraction method of grid positive sequence voltage, using the mathematical method in unbalanced grid distortion even under the condition of extracting the fundamental positive sequence and synchronous phase detection, voltage control. The algorithm through two mathematical transformation to eliminate voltage negative sequence and harmonic components, obtained positive sequence voltage components, avoid adding resonant controller the complexity of the system is reduced. The unbalanced state of microgrid inverter control strategy research for the realization of the micro grid with the grid voltage drop and The operational requirements of the system's unbalanced capability provide theoretical support.
This paper analyzes the principle of droop control, the droop control active and reactive power can not be completely decoupled, the problem of reactive power distribution is not accurate, the micro grid inverter droop coefficient correction algorithm, to achieve active and virtual impedance control combination algorithm, reactive power decoupling to improve the accuracy of reactive power distribution the simulation results verify the effective effect. The feasibility and validity of this method.
Finally, this paper developed the capacity for micro grid inverter prototype based on LCL filter 250kVA, the inverter using low pass filter method to calculate the effective value of voltage, mathematical transformation method to obtain the grid voltage synchronization phase, and the control strategy of voltage feedforward control and damping control combination, to achieve reactive power compensation, black start network operation mode switching to islanded operation mode, according to the user demand for energy storage battery device of constant power, constant voltage, constant current charge and discharge of a variety of strategies, effectively control the function of network side current unbalance in power grid. Based on the developed prototype, experimental study on various conditions, experimental results prove the provided the inverters control effectiveness and correctness of the strategy.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM464

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