三相PWM逆变器的虚拟同步发电机控制方法研究

发布时间：2018-03-05 12:09

本文选题：三相逆变器　切入点：虚拟同步发电机　出处：《哈尔滨工业大学》2016年硕士论文　论文类型：学位论文

【摘要】：对于分布式发电设备,既要并网时跟踪功率给定,又能在电网故障时孤岛运行保证重要负荷的供电。而矢量电流控制方法只能并网运行,孤岛时通常采用下垂控制,模式切换时由电流型控制变为电压型控制,结构复杂。矢量控制过快的响应还导致像LC谐振等稳定问题。而虚拟同步发电机(VSG)是电压型控制,并网孤岛均可,并离网切换时快速且电流无冲击。不同于下垂控制,VSG控制加入虚拟惯量和频率阻尼,可以调节功率的响应时间,减小电流冲击,提高功率和频率的抗扰能力及系统的稳定性。弱电网下,VSG还能支撑电网电压的频率和幅值。本文首先建立了三相PWM并网逆变器在三相静止、两相静止和同步旋转坐标下的电路模型,介绍了虚拟同步发电机控制的原理和传统控制结构,鉴于锁相环带来的稳定问题,提出了正常运行中不用锁相环且电压参考由幅值乘功角得来的控制结构,并在无功控制的前向通道加入一阶惯性来增加稳定性。根据并网时频率偏差小于1%的稳态要求,得到频率阻尼的选取原则,由简化一阶惯性环节的调节时间或二阶系统的阻尼大小和调节时间来确定惯量。虚拟同步发电机控制回路为二阶系统,不同的阻尼大小会使动态响应不一样,比如阻尼太大导致调节时间变长,太小又会引起超调。本文分析了功率阶跃时虚拟惯量、阻尼大小对有功功率和频率响应的影响,无功控制PI系数和惯性常数对无功功率和幅值响应的影响。预同步控制用于发电设备无冲击并入电网,分析了现有方法的缺点,改进的方法中加入相角差滤波,频率参考中减去其比例,就能将相角差调至零附近,减小了启动电流和功率反向。另外功率反向也可加入频率下垂环节,改变系数大小和正负来抑制。常规PWM变换器控制的稳定性问题包括高频谐振和次同步振荡,而虚拟同步发电机存在工频振荡。本文分别建立了有功功率-功角和无功功率-幅值控制的开环传函,得到了整体的矩阵开环传函,用波特图分析发现在50Hz处存在谐振,采用虚拟阻抗和电流高通反馈抑制了工频振荡。为了验证理论分析和所提方法在实际环境中的可行性,在现有的15kW三相PWM并网逆变器实验平台上作了验证。完成了传统和所提虚拟同步发电机控制方法的稳态、动态响应、并离网切换、预同步控制和抑制工频振荡的实验,实验结果表明分析和所提方法的有效性。
[Abstract]:For the distributed generation equipment, it is necessary to track the given power when connected to the grid, and to ensure the power supply of important load by island operation in the event of power network failure. However, the vector current control method can only be connected to the grid, and sagging control is usually used when the power is isolated. In mode switching, the current mode control becomes voltage mode control, and the structure is complex. The quick response of vector control also leads to stability problems such as LC resonance. The VSG control can adjust the response time of power and reduce the current shock, which is different from that of VSG control with virtual inertia and frequency damping. In this paper, a three-phase PWM grid-connected inverter is established in this paper, which can also support the frequency and amplitude of the grid voltage. The circuit model of two phase stationary and synchronous rotation coordinates is introduced. The control principle and traditional control structure of virtual synchronous generator are introduced. In view of the stability problems brought by PLL, A control structure without phase-locked loop and voltage reference obtained from amplitude-multiplying power angle in normal operation is proposed, and the first-order inertia is added to the forward channel of reactive power control to increase stability. According to the steady-state requirement of frequency deviation less than 1% in grid-connection, The selection principle of frequency damping is obtained. The inertia is determined by simplifying the regulating time of the first order inertial link or the damping and regulating time of the second order system. The control loop of the virtual synchronous generator is a second order system. Different damping levels make dynamic response different. For example, too much damping results in longer adjustment time, too small damping and overshoot. In this paper, the influence of virtual inertia and damping on active power and frequency response in power step is analyzed. The influence of Pi coefficient and inertia constant of reactive power control on reactive power and amplitude response. Pre-synchronous control is used to integrate the generation equipment without impact into the power network. The shortcomings of the existing methods are analyzed, and the phase angle difference filter is added to the improved method. By subtracting its proportion from the frequency reference, the phase angle difference can be adjusted to near zero, which reduces the starting current and power reverse. In addition, the power reverse can also be added to the frequency droop link. The stability problems of conventional PWM converter control include high frequency resonance and subsynchronous oscillation. In this paper, the open-loop transmission function of active power angle and reactive power amplitude control is established, and the integral matrix open-loop transmission function is obtained, and the resonance at 50Hz is found by Porter diagram analysis. Virtual impedance and current high pass feedback are used to suppress the power frequency oscillation. In order to verify the feasibility of the theoretical analysis and the proposed method in the actual environment, Based on the existing experimental platform of 15kW three-phase PWM grid-connected inverter, the experiments of steady-state, dynamic response, off-grid switching, pre-synchronization control and suppression of power frequency oscillation of traditional and proposed virtual synchronous generator control methods are completed. The experimental results show that the proposed method is effective.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM464;TM31

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